Game engine supporting many 3D/2D formats and graphic effects
Orx: Data-Driven Game Engine
Arianne is an engine to develop multiplayer online games like Stendhal
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.
The imaginary eight-bit machine
A cross platform Lua based game engine
8-bit Graphical API for Java
Portable game engine with main focus on point-and-click adventures
Build Cross-platform Applications
C/C++ , PHP, PYTHON, 3D ENGINES, CHROME NATIVE CLIENT
3D .NET engine for Windows, Linux, Mac
A game engine written in the D programming language
An advanced flexible game engine for Java.
Single-/multi-player card game Mau Mau (similar to UNO®)
Java decentralized cross-platform network multiplayer game engine
THIS SOFTWARE IS IN PRE-PRE-PRE-PRE-ALPHA. So don't really download it
A generic 2D engine for any kind of game
TurboSphere is an easy to learn and powerful JS based game engine.
Take the chess graphism, and use it with a chess engine.
A multiplatform game engine for interactive fiction experiences
A world editor for HGE game engine written in python and uses OpenGL.
3D game engine for C and C++
A graphics engine + toolkit.