The best open source games on GitHub are free to play, free to study, and free to modify, which makes them a different kind of game library: you can enjoy the game and also open the code to see how it was made. This guide picks five standouts, from a chess server used by millions to the original DOOM source code, with what each one offers players and what game developers can learn from it. Star counts were checked on GitHub on 30 October 2026 and change daily.

DOOM (id-Software/DOOM, 19,819 stars, C++) is the original DOOM open source release, and it remains one of the most studied codebases in gaming. Playing it is only half the point: developers have learned engine architecture, rendering, and game loops from this code for decades, and the community has built countless ports and mods on top of it. It suits retro gaming fans and developers who want to understand how a landmark first-person shooter was actually put together.

Lichess (lichess-org/lila, 18,924 stars, Scala) is the code behind lichess.org, the forever free, adless, and open source chess server. You can play chess against people or engines, solve puzzles, and study games, all without ads or subscriptions, and developers can study how a large, real-time multiplayer service is built. It suits chess players of every level, and it is a rare example of an open source project that competes directly with commercial platforms on quality.

OpenRA (OpenRA/OpenRA, 17,688 stars, C#) is an open source real-time strategy game engine for early Westwood games such as Command & Conquer: Red Alert. It rebuilds those classics for modern systems, with online multiplayer and mod support, so you can play the games you remember without wrestling with old installers. It suits strategy fans and modders best, and developers can learn how an RTS engine handles units, pathfinding, and multiplayer synchronisation.

Dungeon Crawl: Stone Soup (crawl/crawl, 3,054 stars, C++) is the official repository for a deep, turn-based roguelike dungeon crawler that has been developed by a community for years. Every run is different, death is permanent, and the game rewards careful, tactical play over reflexes. It suits players who like long, thoughtful games, and developers can study how procedural dungeons, items, and monster behaviour are balanced over thousands of runs.

Teeworlds (teeworlds/teeworlds, 2,652 stars, C++) is a retro multiplayer shooter with fast, simple, cartoon-style combat that runs on modest hardware. It is smaller than the other games here, but that is part of its charm for developers: the codebase is approachable enough to read, modify, and learn multiplayer game programming from, and the game itself is quick to pick up for a few rounds with friends.

How should you approach open source games? If you only want to play, look for the Releases section on each repo page and download the installer for your system, or play in the browser where offered. If you want to learn, clone the repo, read the README, and try changing one small thing, such as a game speed or a colour, before attempting anything bigger. And check each project's licence before reusing its code or assets in your own game, because open source does not always mean unrestricted use. For more open source projects beyond gaming, see our GitHub directory: Top GitHub Repositories Directory.

FAQ: Are open source games really free? Yes to play and study, under each project's licence, though some projects accept donations and a few use assets with separate terms, so check the repo. FAQ: Do I need to know programming to play them? No. Most offer ready installers or browser play, and coding is only needed if you want to modify them. FAQ: Which game is best for learning game development? Teeworlds for approachable multiplayer code, and DOOM for engine history, depending on what you want to learn.