WikiBattle - 1v1 race who first reaches a randomly selected article.
OneLife - Multiplayer survival game of parenting and civilization building.
OpenMW - Open-source open-world RPG game engine that supports playing Morrowind.
OpenDiablo2 - Open source re-implementation of Diablo 2.
Pioneer - Game of lonely space adventure.
openage - Free (as in freedom) open source clone of the Age of Empires II engine.
AIDungeon2 - Infinite adventures await.
Games on GitHub - List of popular/awesome videos games, add-ons, maps, etc. hosted on GitHub. Any genre. Any platform. Any engine.
Gameboy.Live - Basic gameboy emulator with terminal "Cloud Gaming" support.
HSTracker - Deck tracker and deck manager for Hearthstone on macOS.
MultiMC - Custom launcher for Minecraft that allows you to easily manage multiple installations of Minecraft at once.