Here is an overview over all the retroclones and OSR systems based on the various editions of D&D as well as other RPGs that are based in D&D in one way or the other. A thank you goes to the RPG.net community for helping with this list.
27th Edition Platemail is a retroclone of the Chainmail miniature combat rules whose fantasy supplement lay the foundation for OD&D. Rules for magic are available as well.
Original Dungeons & Dragons
Arrows of Indra is a clone of OD&D modified for a faux-Indian setting. It uses re-skinned versions of the basic D&D classes and a (much-debated) caste system for human subraces.
Bandits & Basilisks is a very rules-light clone of OD&D. Its bestiary features only two creatures, the eponymous bandit and basilisk.
Bandits & Battlecruisers is a science fiction OD&D clone based on Bandits & Basilisks an Terminal Space, an official OD&D supplement made by the same author.
Delving Deeper is another OD&D clone focussing on the first three booklets only. Compared to the Swords & Wizardry White Box, it is less streamlined and includes more material from the original third booklet, like underworld exploration.
Epées & Sorcellerie is a French OD&D retroclone. It is not a straight clone and adds some additional material, like a skill system. An English translation is available as well. The second edition has not been translated yet, though.
Full Metal Plate Mail is a straight OD&D clones with as little alterations made to the rules as necessary. It also includes rules clarifications and material from Outdoor Survival and Chainmail to fill so gaps.
The Grey Book is a compilation the original three OD&D booklets and a much (but no all) of the material published later as well as bits from AD&D.
Grey Matter is a clone of OD&D that adds a large number of classes, spells and monsters while keeping the rules simple.
Grey Six is a streamlined and expanded clone of OD&D. It is based on Grey Matter focusses on low-level play and incorporates aspects from later D&D editions, like a skill systems, themes or character backgrounds.
Humanspace Empires is a RPG based on OD&D and Empire of the Petal Throne. It is intended for games set in the Tékumel setting written by M. A. R. Barker (formerly known as Philip Barker and author of Empire of the Petal Throne).
Microlite74 is a minimalist RPG system that aims at recreating the feel and style of OD&D. Three versions (Basic, Expanded, Standard) exist which each one adding some additional material.
Primordial ODD is an OD&D version that simplifies the game even further, e.g. only two classes - fighter and mage - exist. The system is still in the making.
Renegade is a clone of OD&D with influence from other incarnations of D&D and a focus on campaign building.
Seven Voyages of Zylarthen is a clone of the original three booklets with a few aspects taken from Greyhawk and a couple of own ideas. Seven Voyages of Zylarthen takes inspiration from many sources, including science fiction, Arabian Nights, the legend of King Arthur and more.
Shinobi & Samurai is a game based on OD&D but simplified even further. It is designed for campaigns in an Oriental setting.
Swords & Six-Siders is based on OD&D, but modified in a fashion that the game only requires a six-sided die.
Swords & Wizardry is a streamlined clone of OD&D. The White Box version is based on the three original OD&D booklets. The Complete version adds all the material from the OD&D supplements (Greyhawk, Blackmoor, Eldritch Wizardry). The Core Rules are in-between and contain some material from the three supplements.
Torch & Sword is a minimalist OD&D retroclone that focusses on the three original booklets.
The Complete Warlock is what boils down to an unauthorised compilation of parts of the original OD&D booklets with a few new spells and rules thrown in. The Complete Warlock was published as early as 1975 but evolved into a system of its own later on.
Warriors of the Red Planet is an OD&D OSR game. Instead of being set in a faux-medieval fantasy world, it is set on the eponymous Red Planet and draws inspiration from the John Carter stories (like OD&D did too).
As the name implies, Whitehack is a system based in the OD&D White Box. It includes some significant changes, though, like an alternate magic system.
X-Plorers is a science fiction-themed retroclone of OD&D with the classes and other aspects of the game modified to fit the setting.
Basic Dungeons & Dragons
Adventurer Conqueror King is based on B/X D&D. It is not a straight clone, though, and adds number of options, like variant classes for non-human races. Domain management is supported as well.
Arcana Rising is an RPG that uses the same engine as Hulks & Horrors for urban fantasy games. It depicts heroes with supernatural powers new to humanity against aequally newly awakened supernatural threats.
Aventuras en la Marca del Este is a Spanish-language clone of B/X D&D. One of its supplements, the so-called Green Box, expands the system and includes elements from the Rules Cyclopedia. And English version of Aventuras en la Marca del Este is in the working.
Basic Fantasy RPG is a very slim, toolkit-like version of D&D. While using the d20 mechanic, it is rather basic, takes elements from Mentzer BD&D and does not include many aspects found in D&D 3.5.
Blueholme emulates of the Holmes version of the BD&D rules.
B/X Companion is the third volume of the Moldvay/Cook set that was never officially published. It contains material like high-level play and domain management.
Like the B/X Companion, the Companion Expansion aims at creating the never-published third volume of the Moldvay/Cook BD&D version. It also contains new monster, items and rules for high-level play.
Dangers & Dweomers is a system based on the Rules Cyclopedia. It is significantly shorter, though, and also influenced by Swords & Wizardry and Basic Fantasy RPG. An expanded version called the Blue Book is available as well.
Dark Dungeons is a retroclone of the BD&D Rules Cyclopedia. It also contains additional material, like the expanded Immortals rules from the BECMI rules.
Darker Dungeons is a variant of Dark Dungeons. Whereas Dark Dungeons sticks close to the source material, Darker Dungeons contains house rules and other alterations.
Donjon de Poche is a very slim French retroclone of BD&D. It covers the Basic Set as well as the Companion (in a small expansion).
Exemplars & Eidolons is a slim BD&D retrolcone with three classes (warrior, rogue, sorcerer). However, the game's true purpose is to serve as a template for your own homebrew OSR game. The game uses ideas and images from previous games written by author Kevin Crawford.
HOG - short for Holmes' Other Game - is a very slim retroclone based on the Holmes version of BD&D. It does not contain elaborate lists of monsters, treasures and spell, but rules to create them. A slightly more complex expansion named Advanced HOG is available as well. The PDF also contains rules for Space HOG, a science fiction variant of the HOG.
Holmes77 is a straight clone of the Holmes BD&D rules from 1977. As BD&D is derived from OD&D, Holmes77 clarifies the rules and lays them out in a re-organised manner.
The Holmes Companion is not directly a clone of Holmes BD&D, but rather an expansion to allow play beyond level three without using AD&D 1e. A such, it takes parts from AD&D 1e, but simplifies them to keep the feeling closer to OD&D and BD&D.
Hulks & Horrors uses an engine modelled after BD&D, but is intended for space ship exploration instead of dungeon crawling.
Kazamaták és Kompániák is another Hungarian fantasy RPG. It is mostly a straight clone of BD&D with some minor adjustments and modifications here and there.
Labyrinth Lord is a retroclone of the Moldvay version of BD&D. It aims at emulating its source material, whereas its expansion, the Advanced Edition Companion, adds options from AD&D 1e.
Lamentations of the Flame Princess is a tight B/X retroclone known for its much-discussed gory illustrations.
Machinations of the Space Princess is a science fiction RPG based on Lamentations of the Flame Princess.
Mazes & Perils is a clone of the Holmes version of D&D.It expands the original rules and allows player character to advance beyond the range of levels covered in Holmes BD&D.
Small But Vicious Dog is an RPG based on BD&D and Warhammer Fantasy Role-Play with a mean-spirited design philosophy.
Space Madness is a BD&D-based system for space exploration adventures. All player characters are also space pilots with space ships being a part of rules and character advancement.
Star Wars Galactic Adventures is a retroclone of BD&D for games set in the Star Wars universe. The game is discontinued and the official homepage abandoned, however.
There's Always A Chance (also known as TAAC) is a variant of BD&D with mechanics requiring a d20 roll-under check for almost everything. It also includes some other tweaks. An alternative link to the game can be found here.
Treasure Hunters is a B/X clone intended for fast-paced games. The players take the roles of heroic wealth-gathering adventures. Treasure Hunters does not stray too far away from its base and is still compatible with older D&D material.
Wizards, Warriors & Wyrms is clone of the Holmes version of BD&D that incorporates elements from The Holmes Companion to allow play beyond the third level.
Advanced Dungeons & Dragons 1st Edition
Adventures Dark and Deep is not actually a clone of AD&D 2e. Instead, it is AD&D 2e how the authors think Gary Gygax would have written it. It contains classes published in Dragon and rule changes Gygax hinted at before he left TSR.
Adventures in Fantasy is a discontinued system by Dave Arneson and Richard Snider. It is based on AD&D 1e, but includes some heavy changes like the reduction of the number of classes to two and a loose magic point-based casting system. A review can be found here.
Astonishing Swordsmen & Sorcerers of Hyperborea (the OSR game with the longest name so far) is a modified AD&D clone intended for swords & sorcery instead of high fantasy. Non-human races are not available for player and classes have been changed accordingly.
Balrogs and Bagginses is a variant of AD&D 1e for campaigns set in Tolkien's Middle Earth. The system is mostly independent, but the author recommends to use it together with other D&D books for spells and monsters.
The Challenges Game System is a very light, streamlined clone of AD&D 1e. It was written by BD&D author Thomas Moldvay in 1986, making it one of the oldest retroclones (and not really retro, actually). The system is long out of print, but a review with some more details can be found here.
Fantastic Heroes & Witchery is an OSR game mostly based on AD&D 1e with some elements from other editions included as well. It is streamelined and drops a number of optional rules.
Microlite 78 is a slim RPG based on AD&D 1e. It is (spiritually) based on Microlite 74, a slim and simple clone of OD&D. Microlite 78 makes some notable changes compared to AD&D. The number of stats is reduced to four, monks and bards are absent and class abilities have been reworked.
The Advanced Edition Companion incorporates new options and variant rules, turning the system into something closer to AD&D 1e.
OSRIC (short for Old School Reference & Index Compilation) is a straight retroclone of AD&D 1e. It is supported by a large number of adventure modules and a number of supplements.
Project 74 is an old-school game based on AD&D 1e and addresses common complains about AD&D. It simplifies the system and removes a number of rules, but leaves all core aspects intact.
Scarlet Heroes is an Oriental-themed OSR game intended for a game master with a single player. The power level of the player character has been increased to make the system compatible with old modules.
Advanced Dungeons & Dragons 2nd Edition
For Gold & Glory is a retroclone of AD&D 2e still in the making. For Gold & Glory focusses on the content of the Player's Handbook, but also contains material from the Dungeon Master Guide and the Monstrous Manual.
Hackmaster is an RPG based on AD&D 2e. The fourth edition (the first two editions are non-existent and the third one is a fictional RPG from a series of comic strips) is a parody of many iconic aspects of D&D. Hackmaster is licensed RPG but is now out of print.
Dungeons & Dragons 3rd Edition
Amazing Adventures uses the SIEGE system from Castles & Crusades to power pulp adventures.
Castles & Crusades aims are re-creating the feeling of AD&D 1e, but uses D&D 3.5 mechanics to do so.
d20 Rebirth is an RPG system based on D&D 3.5 with the goal to fix its flaws and be an alternative to D&D 3.5 and Pathfinder. It originates from a thread on the Giant in the Playground forums but has its own forums by now. While there still is some activity, the game is probably discontinued as this point and stuck in alpha phase.
Fantasy Craft is a fantasy RPG originally derived from Spy Craft, but now closer to D&D 3.5 in style and spirit.
Legends & Labyrinth is the original working title of The Secret Fire©™® and quite a different game in some regards. The game is overall closer to its D&D 3.5 parent. Legends & Labyrinths was never completed and the core books (The "Black Book") lacks commissioned art and a bestiary.
Mages & Monsters combines OSR simplicity with streamlined and cohesive and design of post-2000 D&D. The system is still under development, but expanded rules which add many, many options are already available.
Microlite20 is an clone game based on the d20 SRD. It simplifies the game quite a bit. Half the stats are gone, removes all classes but the classic four, and reduces the number of races, spells and abilities. This game spawned a number of spin-offs for other D&D versions.
MyD20 Lite is a simplified version of d20/D&D 3.5. It removes a number of d20 elements and simplifies the rest for a faster and less complicated game.
New Feierland is a light version of D&D based on the d20 rules. It comes with its own setting about the exploration of a colony and is vaguely inspired by Lovecraftian fiction.
Pathfinder is a popular retroclone of D&D 3.5 and undoubtedly the commercially most successful one. It is supported by a large number of supplements and adventures modules.
Trailblazer is a retroclone that aims at fixing the mathematical problems D&D 3e (and d20 systems in general) has. The basic game works like a player's handbook for D&D 3e excluding most spells.
Dungeons & Dragons 4th Edition
Basic D&D 4e is a very slim retroclone of D&D 4e. It strips the four traditional D&D classes (fighter, cleric, mage, thief) down to the essentials, removes many powers and feats and reduces the tactical combat aspect. The game remains compatible with 4e adventure modules, monster and other material, though.
Eldritch Worlds is not a straight D&D 4e clone, but embraces 4e's strengths. The system has a variety of races, classes and implements tactical combat. While material for classic high fantasy campaigns is there, the game also supports other settings.
Fourth Edition Reborn (like its predecessor Magic Sword: Fourth Edition Reborn) is a sequel-like D&D 4e retroclone. It is probably discontinued.
4th Trifold is a system based on D&D 4e with minimalist core rules. Like the original game, it is designed for tactical cinematic combat. 4th Trifold is intended for high fantasy games, but the core rules can be used for other campaigns too.
Strike! is a d6-based tactical combat RPG. It is a continuation of The Scared BBQ, a D&D 4e clone. Strike! simplifies the 4e rules and consist of core rulebook as well as a couple of supplements that support fantasy, science fiction and Lovecraftian campaigns.
The Sacred BBQ is a system based on D&D 4e. Its name is derived from the intention of the author not to be reluctant when it comes to butchering D&D's holy cows.
Dungeons & Dragons 5th Edition
At this point, we are not aware of any cones based on D&D 5e. However, D&D 5e has been released quite recently, so give the community some time and the clones will roll in eventually.
More games based on Swords & Wizardry:
Ancient Mysteries & Lost Treasures is based on the White Box as well as the Core Rules. It is written for adventures in a modern setting with adventures similar to Indiana Jones.
Backswords & Bucklers is a clone of the Swords & Wizardry White Box set in Elizabethan England.
Blood & Bullets is Swords & Wizardry rewritten for adventures set in the Old West. It features several classes like gambler or tribal warrior, rules for firearms (obviously) and an Old West bestiary.
The Blue Book of Dangers and Dweomers is based on the Swords & Wizardry Core Rules, but adds additional races, class options and material inspired by D&D 3.5. It uses a d6-based resolution system.
Crimson Blades is a game based on Woodland Warriors which in turn is based on Swords & Wizardry. It is set in a dark fantasy world, the Crimson Lands, and is intended for swords & sorcery-style campaigns. Crimson Blades is d6-based.
Crypts & Things removes all non-human races and adds additional fighting styles and modified spellcasting classes to give the game a feel closer to swords & sorcery instead of high fantasy.
Hideouts & Hoodlums is the first superhero RPG to use Swords & Wizardry as a base. It aims at emulating the feel of the Golden Age of comic books.
Mystery Men! is another superhero game that uses a modified version of Swords & Wizardry as a base.
Pars Fortuna is a system based on Swords & Wizardry. It retains the OD&D core while at the same time replacing standard races, classes and other elements with ones generated with random online generators
Rædwald is a variant of the Swords & Wizardry White Box intended for games set in an Old English setting. The game sets the mood for an Anglo-Saxon campaign rather than being a historical game, though.
Ruins & Ronin is a Asian-themed modification of the Swords & Wizardry White Box. It is not an expansion, but a complete game by itself.
Sabres & Witchery is written for games set in the late 17th to early 19th century. The players assume the role of demon hunters that deal with supernatural forces and creatures.
Seeded Space is a space-themed game based on Swords & Wizardry. It is set in a distant galaxy many years into the future. Seeded Space features a number of playable races (including aliens, animal hybrids and artificial life forms) and rules for psionics.
The Siege Perilous is based on the Swords & Wizardry White Box. It was written to support games inspired by the early Ultima games instead of generic high fantasy campaigns.
Stone & Wood takes Swords & Wizardry and places it in the world of The Chronicles of Thomas Covenant, a series of high fantasy novels by Stephen R. Donaldson.
Woodland Warriors is an OD&D clone based on Swords & Wizardry. It is modified to suit play as anthropomorphic animals.
More games based on Labyrinth Lord:
Engines & Empires uses the Labyrinth Lord rules to power games set in a steampunk setting inspired by the Victorian era.
Mutant Future is a futuristic, post-apocalyptic system inspired by Gamma World but using the Labyrinth Lord rules.
Starships & Spacemen is suited for Start Trek-like games and uses the Labyrinth Lord core with adequate modifications.
Retroclone websites with game book-like content:
Beyond Heroes is an RPG compatible with D&D editions from OD&D to AD&D 2e. The system is intended for all kinds of settings, including modern or futuristic ones.
Donjon offers a narrative dungeon exploration system with the spirit of old-school D&D.
FATEsy Heartbreaker aims at recreating the style and feeling of D&D with the FATE Core engine.
Other systems not directly tied to one single edition:
13th Age is a a system derived from D&D 3.5 and D&D 4e. It uses a modified version of the d20 system while being closer to D&D 4e in regard to character design.
3D6 in Order started as a set of house rules for Swords & Wizardry, but has become its own system since. It goal is to be accessible and get the game started quickly.
Advanced Dungeons & Dragons 3rd Edition is what that D&D edition should have looked like according to the author. The systems is based in AD&D 1e and 2e with elements from D&D 3.X as well as Castles & Crusades.
Back to the Dungeon is a D&D-inspired RPG. Most player character rules come from BD&D, material for the game master is taken from OD&D and rules from Microlite 20 are thrown in as well. The game comes in five retro-style booklets.
Beyond the Wall is an old-school game inspired by the works of Ursula K. LeGuin and Lloyd Alexander. It offers ready-made scenario packs for play with little preparation time.
The Big Brown Book is not a OD&D retroclone, but a variant that explores what OD&D could have looked like if it had stuck closer to its Chainmail war game roots.
Blood & Treasure is an RPG with elements from all editions of D&D.
Blood, Guts & Glory, formerly know as Darkest Dungeons, is set in a post-apocalyptic Elizabethan England. While spiritually connected to Dark Dungeons and Darker Dungeons, it combines elements from D&D 3e and Rolemaster.
D100 is a D&D-sytle game with mechanics that exclusively uses the d100 to resolve everything.
Dark Sun OSR Hack is rules-light D&D system based on the New Feierland d20 hack. As the name suggests, it is written for games set in the world of Dark Sun.
Dragons at Dawn is a vaguely D&D-like fantasy RPG with the premise of re-creating the fantasy rules that Dave Arneson used for his games in the pre-D&D times. The system has been criticised for not actually sticking to what Arneson said about his personal system and abusing his name. Dragons at Dawn is currently unavailable. Its successor is Champions of Zed, which is yet to be published.
Errant RPG is a modern take on D&D. It combines the simplicity of older D&D editions with the modern design of the newer ones.
Flying Swordsman is not directly based on AD&D 2e, but inspired by Dragon Fist, a wuxia martial arts game derived from AD&D 2e that was never published.
Forward to Adventure! is a system based on old editions of D&D. It also includes elements from modern editions, though, as well as changes of its own, such as a collective combat system.
Ghastly Affair is a D&D variant that runs on a d20-derived engine. It focusses on Romantic Gothic themes and has an appropriate class and monster selection. The core book also contains a lot of random tables and inspirational stuff.
Go Fer Yer Gun! is a stripped-down Old West RPG based on d20. It leaves out many of the aspects of d20, like feats and skills, though. A expansion for Old West fantasy roleplaying named Wizards & Winchesters is in the making.
Heroes against Darkness is an RPG taking elements for all editions of D&D. The mechanics are closer to D&D 3.5 and D&D 4e with the spirit being closer to OD&D.
The Holmes Screen is a clone of the Holmes version of BD&D in form of a game master's screen that allows character advancement up to level nine.
Mazes & Minotaurs is a game inspired by OD&D. Its theme is ancient Roman and Greek mythology rather than high fantasy. Two versions exist: One closer to OD&D, the other one a bit more complex. It also has a viking-themed spin-off.
Medieval Mysteries uses the same engine as Go Fer Yer Gun! to power games focussing on solving mysteries in medieval England.
Necrophylax is a zombie survival horror RPG. It is derived from older versions of D&D, but not a clone of any distinct edition.
Old Dragon is a Brazilian old-school RPG. While clearly inspired by BD&D, the first D&D edition published in Brazil, it also has elements closer to AD&D and D&D 3.5.
Oltréé is a French RPG that captures the mood and style of old-school D&D, but slightly deviates from it when it comes to mechanics.
1 Pot RPG is a minimalist D&D clone that combines character sheet and rules into a single cheat sheet that contains all the rules needed to run a game.
Other Dust is an old-school RPG suited for games in a post-apocalyptic setting. It uses the same system as Stars Without Number.
Owl Hoot Trail is a system originally based on Microlite74. It is written for games set in a fantasy Old West.
Peril is a minimalist fantasy RPG alternatively also called Pocket Full of Peril. It is a mix between Searchers of the Unknown and Microlite74 with a number of modifications.
Peryton is a d20-based retroclone. It does not, however, aim at emulating D&D 3e, but instead recreates the feel of old D&D editions while streamlining them at the same time.
Radiance is a modified hybrid of D&D 3.5 and D&D 4e. Its goal is to provide balanced classes and streamlined design while retaining classic D&D tropes.
Red Box Fantasy is a D&D retroclone that aims at capturing the spirit of old-school D&D, but also includes some revised rules closer to d20.
Red Box Hack is based on the Mentzer version of BD&D, the so-called Red Box. It started out as a clone of the Red Box boiled down to its most iconic elements, but has become a system of its own by now.
Ruins & Riches emulates D&D-style dungeon exploration with D&D classes and tropes, but uses a simplified engine.
Searchers of the Unknown is a minimalist D&D-inspired RPG that fits on one page and does not require more than the character sheet. A variant named Hobbits in the Unknown is special designed for playing as hobbits.
Shotguns & Saddles is an RPG set in the Old West based on OD&D. It includes a number of modifications, though, and provides additional rules for duels and other special occasions.
Spears of the Dawn is based on old D&D editions, but does not focus on faux-Medieval play but on an Africa-like setting instead.
Spellcraft & Swordplay is based on OD&D, but incorporates elements from Chainmail as well as Supplement I: Greyhawk.
Stars Without Number is a science fiction RPG with an engine largely derived from OD&D and BD&D.
Tales of the Space Princess is a rules-light RPG inspired by old D&D version but intended for games set in pulp and retro science fiction settings.
Tombs & Terrors is system that uses an engine based on Castles & Crusades, but aims at capturing the feel of older editions of D&D.
More games based on Searchers of the Unknown
Cybermorphs is a one-page science fiction RPG that retains only the most basic elements of D&D 3e, such as hit dice, ascending armour class and the d20 resolution mechanics. The player take the role of the titular cypermorphs, huge biotech robots that grow stronger by absorbing parts of their foes.
No Bloody Heroes is a slim one-page RPG. While similar to OD&D and BD&D, it also lifts elements from D&D 3e and brings in some new ideas (like a d6-based sabing throw system). There are no character classes; instead, player character are defined by actions and equipment. There is also a supplement with hexcrawl tables called No Bloody Rangers.
Inspired by films such as Quel Maledetto Treno Blindato, The Bastards depicts the player characters as Allied soldiers that do anything from stealing Nazi gold, abducting Nazi scientist or assassinating Hitler.
If that's not enough Searchers of the Unknown for you, this PDF here compiles 50+ slim systems based on it.
Games that catch the spirit of D&D, but use different mechanics:
Ability Score is a super-slim system (on just two pages) with an engine based on the six classic D&D ability scores. The engine is not unlike the one in the World games and supports magic, psionics and all kinds of settings, like science fiction, horror and fantasy.
Fenris 2d6 is a game based OD&D. It uses the titular 2d6 mechanic instead of the usual 1d20 mechanic, though.
Adventure Fantasy Game uses a different, d6-based engine, but keeps the style and feeling of old-school D&D.
Ambition & Avarice aims at capturing the feel of OD&D, but uses different mechanics. It also comes with a skill system, different race options and more.
Barbarians of Lemuria does not use D&D mechanics, but a 2d6-based system instead. Nevertheless, it combines old-school simplicity with a swords & sorcery setting.
Barebones Fantasy is a fantasy RPG, but does not use D&D mechanics. In stead, it is based on the Star Frontier rules also published by TSR.
Broken Urthe is a system for post-apocalyptic games. It has the spirit of older versions of D&D, but is not a straight clone.
Burning THAC0 is a variant based on The Burning Wheel with the goal of creating an old-school AD&D feeling, fiddly subsystems included.
Crimson Dragon Slayer is an D&D-based RPG based on the 80s, their tropes and all the good and bad stuff that comes attached to them. It is not a pure fantasy RPG and optionally contains science fiction elements.
Deeds & Doers is a slim system with player's guide, game master's guide, character sheet and a sample adventure on a single page each. Its central idea is that rolls are only made rarely and character abilities are mostly roleplayed.
Drowning & Falling is a satirical fantasy RPG that parodies dangerous old-school dungeon crawling and passive-aggressive dungeon design.
Dungeons Crawl Classics combines a lethal gameplay style inspired by OD&D with modern mechanics.
Dungeon Delvers is a minimalist RPG that catches the spirit of D&D on a single page.
Dungeon Squad! is a minimalist RPG with the spirit of old-school D&D. It is intended to be picked up and played with no preparation time. Several alternate editions can be found here, here and here.
Dungeon Slayers used mechanics different from old-school D&D, but aims at the same dungeon crawl feeling.
Dungeon World is not a variant not D&D, but instead uses the engine of Apocalypse World with modifications for a game with the feel of D&D.
Encounter Critical is not an actual retroclone, but instead a fantasy RPG that purposefully pretends to be one.
Fictive Hack is a hack of Old School Hack, which is a hack of Red Box Hack, which is a hack of Mentzer BD&D. It is intended fro adventures in the The World Between setting.
Fire & Sword is a fantasy RPG with some similarities to older editions of D&D. It is not a clone, though, and uses mechanics of its own.
Five Ancient Kingdoms is a system mechanically inspired by Chainmail and OD&D. It is intended for games set in an Arabian Nights setting.
Gods & Monsters is a fantasy RPG. It shares some similarities with D&D, like the ability scores and the classes, but also includes some changes like a modified combat system.
GORE (short for Generic Old-School Role-Playing Engine) is based on the Chaosium BRP system, but uses the magic system and spells from BD&D.
Hackmaster 5th Edition moved Hackmaster away from being a D&D parody clone and towards a D&D-like games with the maximum number of tables, mechanics, exception-based rules and fiddly subsystems shoved into it.
Helvéczia is a Hungarian fantasy RPG influenced by the fairy tales collected by the Brothers Grimm. It is set in a fantasy version of Switzerland and is based on Kard és Mágia.
Kard és Mágia is a Hungarian fantasy RPG supported by a large number of modules. It is not based on any specific version of D&D, but shares its spirit and style.
Legends of the Ancient World is a minimalist fantasy RPG. It is inspired by D&D, but uses a range of altered mechanics more based on Melee and The Labyrinth.
Long Live the Fighting Men and Magic-Users!!! is a very slim game in the spirit of OD&D. It uses different mechanics, though, and is intended primarily for one-shots.
Monsters & Magic is a game with the style and spirit of D&D, but not the mechanics.
Into the Odd is a fantasy RPG focussed on exploration and survival. It uses a system not unlike but distinct from D&D.
Old School Hack is a hack of Red Box Hack (which in turn is a Mentzer BD&D hack). It is a very rules-light system and provides a number of character classes playable out-of-the-box.
Old School Hats is a clone of Old School Hack modified for games set in the Old West.
Retro Phaze, formerly know as Elegia, does not use mechanics directly taken from D&D, but retains elements like ability scores and classes. Thematically, is aims at capturing the feels of old console RPGs like original Final Fantasy and Shining Force.
The Secret Fire©™® is a fantasy RPG with a basic premise similar to D&D. It aims at narrative gaming and bakes roleplaying into mechanics.
Space Ryft uses the same engine as Broken Urthe, but is intended for space adventures.
Sword & Shield is a minimalist D&D-like RPG that is only six pages long.
While Torchbearer is mechanically based on the Mouse Guard RPG, it captures the feel of old-school D&D editions and designed to support dungeon crawling.
Treasure Awaits! is a slim RPG in the spirit of D&D designed to get started in no time. The basic game is made for dungeon exploration, whereas the expansion More Treasure Awaits! includes surface exploration as well.
Tunnel Quest is a rules-light system for dungeon exploration with the occasional monster fight. It intended to be played with children and based on Dragon by Paul Elliott.
Under the Moons of Zoon is a RPG mixing science fiction with pulp fantasy.
Warrior, Rogue & Mage is a fantasy RPG with a D&D feel, but not classes and a different engine.
Wayfarers is another D&D-inspired game that uses different mechanics, but retains the feel of old D&D with elements like D&D-style character classes.
ZeFRS is an old-school game bases on the short-lived Conan RPG published by TSR.