DiaT is a Textadventure
QuadTree JS is a library for game developers
cross-platform 2d game engine
I am working on upgrading the XNA Platform Game Template.
A game engine in java for 2D strategy games
Java game engine for shoot 'em ups, using Java2D.
A C++ library for programmers transitioning from "Game Maker Language"
AS3 Utilities library (Games Development Framework)
A cross-platform OpenGL based lightweight scenegraph library
Text-based adventure game creator and player. Comes with demo games.
SDK for Resident Evil Games
Delphi-like IDE for cross-platform game development
Sourceport of the classic Descent Level Editor
A cross platform 3d c++ game engine
Game framework on top of Python, Panda3D and Twisted
The Lambda-Engine is a cross platform game engine.