Games on GitHub – A list of popular/awesome video games hosted on GitHub
Project is seemingly dead with the latest commit being from 2018.Two major games with code on github I can think of are Amnesia: The Dark Descent (1) and Celeste (2)(1) https://github.com/FrictionalGames/AmnesiaTheDarkDescent
(2) https://github.com/NoelFB/Celeste