Below is a list of open source games and game-related projects that can be found on GitHub - old school text adventures, educational games, 8-bit platform games, browser-based games, indie games, GameJam projects, add-ons/maps/hacks/plugins for commercial games, libraries, frameworks, engines, you name it.
If you'd like to add a repository to the list, please create an Issue, or fork this repository and submit a pull request.
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- Major Companies
 - Browser-Based
 - Native
 - Mobile Games
 - Just The Source
 - Frameworks/Engines/Libraries
 - Maps/Hacks/Plugins/Utilities/All of the Things™
 
A selection of major game studios, publishers, etc. using GitHub:
- 3D Hartwing Chess Set - 3D chess game done in HTML/CSS/JS.
 - Green Mahjong - solitaire mahjong game done in HTML/CSS/JS.
 - Lichess - Free chess game using HTML5 & websockets, built with scala, Play 2.1, mongodb and elasticsearch. Play now!
 - Desperate Gods - a free online board game that was designed to be played just like a board game in real-life: no rules are enforced by the computer. Play it now!
 
- Alien Invasion - space invaders++. Play it now!
 - Asteroids - pure JavaScript asteroids. Play it now!
 - Digger - HTML5 version of a Boulderdash game. Play it now!
 - Coffee Snake - an HTML5 snake game written in coffee script. Play it now!
 - Draconas - a classic shoot 'em up game build with the Three.js library. Play it now!
 - hurry! - a small but speedy arcade shooter. Play it now!
 - Snake - a clone of the snake game. Play it now!
 - Survivor - a playable HTML + CSS + JavaScript remake of a space-based "shoot-'em-up" arcade game for Atari / Commodore 64 from 1982, including a level editor and design tool. Play now!
 - Duck Hunt JS - DuckHunt ported to JS and HTML5 with a level creator. Play now!
 - Mario 5 HTML - infinite Mario in HTML5 JavaScript - using Canvas and Audio elements. Play now!
 - Cell Mates - a GGJ 13 game.
 - Codename Lumberjack - a simple flash game written using Actionscript 3.0 and Flixel. Play it now!
 - Coil - HTML5 canvas game where you defeat enemies by wrapping enemies in your trail. Play now!
 - FlxTeroids - a very simple flixel game inspired by the classic arcade shooter. Play now!
 - EKG Runner - a GGJ 13 game.
 - Emberwind - HTML5 port of the indie platform game Emberwind. Play now!
 - Fluid Table Tennis - renders a table tennis game interacting with a full-color real-time fluid simulation at 60 FPS. Play now!
 - FlxInvaders - a very simple flixel game inspired by the Taito classic. Play now!
 - Grave Robbers - a sort of GIRP-inspired tower defense. Play now!
 - HotFix - help Hotfix collect stargazers and avoid enemies. Collect commits to upgrade hotfix and add new features. Play now!
 - Marble Soccer - a marble game for learning three.js.
 - Mode - a small (but sadly not that simple) demo game built on the flixel framework. Play now!
 - Onslaught Arena - fight off hordes of classic medieval monsters in this fast paced arcade shooter! Play now!
 - Pappu Pakia - an addictive game where you guide little Pappu around obstacles while collecting coins, stars, and berries and avoiding enemies known as Pakias. Play now!
 - PixelPlatformer - simple platformer game that demostrates the power of the Entity game engine.
 - Polybranch - a minimalist 3D game. Dodging branches may seem easy at first, but how long can you hold up as you approach terminal velocity? Play now!
 - Release Cycles - n abstract racing game where you fight against the clock and the computer to get as far as you can in a product's life-cycle. Play now!
 - Ski Free - a JavaScript port of the classic PC Game, Skifree. Play the Demo now!
 - SORADES 13K - a scrolling shooter in the vein of "Raptor: Call of the Shadows" and "Warning Forever". Play now!
 - zedinvaders -a game is based on our original comic ZED, seen inside "zero-episode" called "Game Over". Play now!
 - Crappy Bird - Flappy bird clone in JavaScript and Canvas2D Api Play now!
 - Clumsy Bird - Flappy bird clone in JavaScript using MelonJS Play now!
 
- BananaBread - a port of the Cube 2/Sauerbraten 3D game engine/first person shooter to the web, compiling C++ and OpenGL to JavaScript and WebGL using Emscripten.
 
- Diablo JS - Isometric minimal-code style game at html5 canvas and javascript.
 
- BrowserQuest - an HTML5/JavaScript multiplayer game experiment. Play it now!
 
- Command & Conquer - clone of the popular RTS. Play it now!
 - Tower Defence - 3D Tower Defense build with Three.js in HTML5. Play it now!
 
- Trigger Rally Online Edition - fast arcade rally racing. Play now!
 
- Blk Game - a multiplayer Javascript/WebGL voxel world game demo.
 - Cube Engine - 3D engine completely written in HTML5 without OpenGL.
 
- Hextris - an addictive puzzle game inspired by Tetris. Play now!
 - Orbium - a modern version of the 90's game Log!cal. Play now!
 - Pop Pop Win - an implementation of Minesweeper in Dart.
 
- HeartLine - a GGJ13 game.
 - Squirts - A well-known indie game implemented in JavaScript. Play now!
 - The Killer - a flash/as3-based "nongame". Play it now!
 
- Epic Inventor - an indie, side-scrolling, action, RPG.
 - OpenLieroX - Liero clone, like realtime Worms, or a 2D Quake.
 - Savage Wheels - 2D car crashing game similar to the old classic Destruction Derby.
 
- LWJake2 - LWJGL port of Quake 2.
 - openspades - Compatible client of Ace of Spades 0.75.
 
- Arx Fatalis - cross-platform port of Arx Fatalis, a first-person role-playing game.
 - Open MW - Reimplementation of the game Morrowind.
 - Flare RPG - Fantasy action RPG game with its own engine.
 - Valyria Tear - open-source single-player medieval-fantasy 2D J-RPG.
 
- Commander Genius - Commander Keen compatible clone.
 - Escape of the cat - Hardcore oldschool platformer on INSTEAD.
 - Frogatto - an action-adventure game, starring a certain quixotic frog.
 - Gish - open Source version of the award-winning physics platformer.
 - Journey to the Center of Hawkthorne - This 2d platformer is based on Community's Digital Estate Planning episodebuilt using the LÖVE game engine.
 - Mario-Level-1 - The first level of Super Mario Bros made with Python and Pygame.
 
- 2048-cli - A cli version of the game 2048 for your Linux terminal.
 - Dominion - a C# implementation of Dominion, a board/card game.
 - IRMINGARD - patience card game written in Ruby.
 - PuzzleDash - A match-3 puzzle game built in the Dash engine.
 - Wizznic - most awesome puzzle game.
 
- Craft - A simple Minecraft clone written in C using modern OpenGL.
 - Minetest - An open source infinite-world block sandbox game with survival and crafting.
 - Freeminer - An open source sandbox game inspired by Minecraft.
 
- Caesaria - an open-source remake of the popular citybuilder and economic sim Caesar III.
 - CorsixTH - open source clone of Theme Hospital
 - Unknown Horizons - 2D isometric RTS economic strategy game written in C++ & Python, built on the Flexible Isometric Free Engine.
 - openage - Open source clone of the Age of Empires II engine.
 - OpenRA - an open-source implementation of the Red Alert engine using .NET/mono and OpenGL. Runs on Windows, Linux and OSX.
 - OpenXcom - Open-source clone of the original X-Com
 - PCOTM (Phone Case of the Monster) - A Ruby game, where you play as a phone-collecting monster.
 - Pioneer - A game of lonely space adventure.
 - Polly-B-Gone - a physics platform game about a plucky wheeled robot named Polly.
 - Source of Tales - an entry in the Liberated Pixel Cup 2012.
 - Spring RTS - a powerful free cross-platform RTS engine.
 - Voxeliq - an open source block-based game engine implementation developed with C#.
 - Wizznic - most awesome puzzle game.
 
- ChaseWhisplyProject - Chase Whisply is a FPS. You have to seek, find and kill the ghosts living around you.
 - Green Mahjong - solitaire mahjong game done in HTML/CSS/JS.
 
- Bridges - a puzzle game with bridges, houses, tolls, and subways for iOS.
 - Canabalt - open source release of Canabalt for iOS.
 - Doom - Doom Classic for iOS.
 - DrugsNRock - a simple multiplayer rhythm game designed during the Global Game Jam'13.
 - Frogatto - an action-adventure game, starring a certain quixotic frog.
 - Gorillas - an iPhone (or iPod touch) port of the popular old QBasic game.
 - Light Jockey - an iOS Auditorium-like game.
 - Lumio - a puzzle game for iOS developed using Cocos2D. Available free on the App Store.
 - Wolfenstein 3D - Wolfenstein 3D for iOS Source Release.
 - Green Mahjong - solitaire mahjong game done in HTML/CSS/JS.
 
- Aquaria - a breath-taking underwater fantasy game. Winner of the Grand Prize at the 2007 Independent Games Festival.
 - Doom 3 - pew pew pew.
 - ID Software - includes Doom, Quake, Wolfenstein and more!
 - MaNGOS - a full featured World of Warcraft server!
 - Miner Wars 2081 - for modders of Miner Wars 2081, a 6DOF action-survival space-shooter simulation-game set in the year 2081.
 - Prince of Persia - Prince of Persia!
 
- Akihabara - a set of libraries, tools and presets to create pixelated indie-style 8/16-bit era games in Javascript.
 - ammo.js - direct port of the Bullet physics engine to JavaScript using Emscripten.
 - Babylon.js - a complete JavaScript framework for building 3D games with HTML 5 and WebGL.
 - Chipmunk Physics - a simple, lightweight, fast and portable 2D rigid body physics library written in C.
 - cocos2d for iphone - a framework for building 2D games, demos, and other graphical/interactive applications for iPod Touch, iPhone, iPad and Mac. It is based on the cocos2d design but instead of using python it, uses objective-c.
 - cocos2d-x - a multi-platform framework for building 2d games, interactive books, demos and other graphical applications. It is based on cocos2d-iphone, but instead of using Objective-C, it uses C++. It works on iOS, Android, Windows Phone, OS X, Windows and Linux.
 - Dash - A free and open 3D game engine written in D.
 - Duality - a 2D Game Development Framework.
 - EaselJS - a library to make working with the Canvas element easier.
 - EntityJS - an HTML5 javascript game engine utlizing the entity-component design.
 - Flashpunk - a free ActionScript 3 library designed for developing 2D Flash games.
 - Flixel - an open source game-making library written entirely in ActionScript 3.
 - GenesisEngine - GenesisEngine allows you to create and explore procedurally-generated planetary systems, from ground level all the way out into space. Experiments with procedurally-generated worlds, XNA, and design patterns.
 - Gladiator 3D - Canvas based JavaScript ray casting engine for pseudo 3D games.
 - MonoGame - XNA Implementation for Mono based platforms (supports iOS, Android, Linux, and started work on PS Suite and NaCli ).
 - pixi.js - Super fast HTML 5 2D rendering engine that uses webGL with canvas fallback.
 - Plasma - Cyan Worlds's Plasma game engine.
 - Quasi-Engine - a QtQuick framework that intends to be a complete toolset to ease 2d game development
 - Spring - an Open Source Real Time Strategy game engine.
 - Tesseract - make mapping more fun by using modern dynamic rendering techniques, sothat you can get instant feedback on lighting changes, not just geometry.
 - Torque 3D - MIT Licensed Open Source version of Torque 3D from GarageGames.
 - Turbulenz Engine - an HTML5 game engine and server-side APIs available in JavaScript and TypeScript for building and distributing 2D and 3D games.
 - melonJS - An open-source HTML5 game framework for 2D games.
 
- Bfxr - Flash + AIR sound effects generator. Based on Sfxr.
 - FlxCollisions - a simple set of 2d physics + collision demos for flixel v2.0. Play now!
 - Gamertag - a gem for retrieving Xbox Live Gamertag information from various sources.
 - Halo::Reach::API - Ruby gem for interacting with the Halo:Reach API.
 - Leaderboard (Java) - Leaderboards backed by Redis (in Java).
 - Leaderboard (PHP) - Leaderboards backed by Redis (in PHP).
 - Leaderboard (Python) - Leaderboards backed by Redis (in Python).
 - Leaderboard (Ruby) - Leaderboards backed by Redis (in Ruby).
 - Leaderboard (Scala) - Leaderboards backed by Redis (in Scala).
 - libfreenect - drivers and libraries for the Xbox Kinect device on WIndows, Linux, and OS X.
 - OpenEmu - an open source project to bring game emulation to OS X as a first class citizen.
 - stats.js - JavaScript performance monitor.
 - Tassadar - A Starcraft 2 replay parser written in pure Ruby.
 - World of Warcraft Addons - too many to list!
 - World of Warcraft API Docs - the public documentation for the RESTful web service provided as part of the World of Warcraft community site.
 











