A dead simple 2D game engine for Go
High performance UI layout library in C
A game engine powered by python and panda3d
JavaScript-based game engine designed to empower developers
Orx: Portable Game Engine
GemRB is a portable open-source implementation of the Infinity Engine
A modern, cross-platform Quake game engine based on FitzQuake.
Game engine supporting many 3D/2D formats and graphic effects
The multiplayer game engine
State Management and Multiplayer Networking for Turn-Based Games
A cross platform Lua based game engine
Portable game engine with main focus on point-and-click adventures
A generic 2D engine for any kind of game
Free Android 2D OpenGL Game Engine
Open source, moddable game engine for the "Polygon Love 2" game
Little game background framework in java.
Free MMORPG Engine. Develop and host graphical browser-based games.