GitHub is a reflection of current coding trends. While C++ remains a staple for heavy-duty game development, web-based languages dominate the "play-in-browser" category. Why it's used for GitHub Games
You can "Look Under the Hood." If you enjoy a game, you can read the code to see exactly how the physics, AI, or rendering works.
Created by Mozilla, this is a multiplayer RPG that demonstrates the power of WebSockets and HTML5.
The addictive sliding-tile puzzle by Gabriele Cirulli is perhaps the most famous GitHub game. You can find the original source code and thousands of "forks" (variations).
If you want to dive in right now, visit the official GitHub Gaming page to see what is currently trending. You might find anything from a simple CLI (Command Line Interface) dungeon crawler to a full-blown 3D space flight simulator. 16-Games in C++/SFML - GitHub