Highly customizable library for procedural world generation
A cross-platform interpreter for many point-and-click adventure games
A JavaScript game library to quickly develop board games for the web
3D .NET engine for Windows, Linux, Mac
The solution to all your problems
C-Lesh is a game programming language for 2D games.
LEGADEE (LEarning GAme DEsign Environment)
Java based Open source Voxel Engine for RTS games