CTFs as you need them
Arianne is an engine to develop multiplayer online games like Stendhal
JavaScript framework to build game engines, games, emulators and apps
Java Settlers
A synchronisation component for p5.js
Java decentralized cross-platform network multiplayer game engine
Free strategy browsergame engine.
Educational framework for OpenGLES, OpenCL and OpenAL
C-Lesh is a game programming language for 2D games.
Open Source Virtual World and MMOG Development Platform
Investigo - DX9 Performance and Debugging Toolkit