A game engine powered by python and panda3d
Free, open source game engine online
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
KlayGE is a cross-platform open source game engine
Text Based Game Engine and Parser
Tactical, turn-based game engine, that uses OpenGL and WinAPI
Open source, moddable game engine for the "Polygon Love 2" game