Cross-platform C framework very compact libraries and tools.
2D game creation software
A generic 2D engine for any kind of game
A multithreaded, test-driven electronics emulator for .net 4.0.
The Model Railroad System can help you run your railroad.
A train simulator wroten in Java.
opensource clone of Duke Nukem Manhattan Project
TurboSphere is an easy to learn and powerful JS based game engine.
Tongue-in-cheek action RPG
Just another online poker software, but open source for once.