Osu

osu! stable installer for Linux with patched wine-osu and other nice features 8)

The automation tower defense RTS

Open-source, cross-platform 2D/3D/multiplayer game engine designed for everyone.

Desktop/Android/HTML5/iOS Java game development framework

♞ lichess.org: the forever free, adless and open source chess server ♞

Open Source real-time strategy game engine for early Westwood games such as Command & Conquer: Red Alert written in C# using SDL and OpenGL.