RetroArch is a frontend for emulators, game engines and media players.
2D Game Engine
A cross-platform interpreter for many point-and-click adventure games
Multi-platform game engine similar to old Megaman with a stage editor
Paintown is a 2d fighting game engine.
Small OpenGL based game enegine
Pye - Javascript Engine For Drawing Fast, Fluid and Dynamic Pie Charts
Devanagari OCR On Cell Broadband Engine