JavaScript-based game engine designed to empower developers
GemRB is a portable open-source implementation of the Infinity Engine
Game engine supporting many 3D/2D formats and graphic effects
SDL based generic 2D game engine
DOOM / Heretic / Hexen source port with enhanced graphics and UI
Flexible and easy-to-use 2d game engine
Built to be ease of use, with no programming knowledge, Multi-platform
Free MMORPG Engine. Develop and host graphical browser-based games.