Free game engine for development of desktop, mobile, and web games
3D Game engine with editor
scene-oriented, flexible 3D engine (C++, Python, C#, Java)
Descent 3 by Outrage Entertainment
Vivid3D is a C++ IDE/3D engine, with python scripting.
3D C++ Game Engine - yet another open source game engine
A 2D game engine and level editor
KlayGE is a cross-platform open source game engine
Multi-platform game engine similar to old Megaman with a stage editor
A roguelike game engine/editor
3D Game engine
A Simple Game Engine
Tactical, turn-based game engine, that uses OpenGL and WinAPI
Open source, moddable game engine for the "Polygon Love 2" game
cross-platform 2d game engine