PyCAPGE - Python Classic Adventure Point and Click Game Engine
Spring is a free RTS engine developed for Windows, Linux and Mac OS X.
2D Game Engine
FreeCS is a free-software reimplementation of Counter-Strike 1.5.
A real-time game development platform
Multidocument automation by templates - for sphinx, mkdocs, epydoc ...
Gorgon Game Engine (GGE) is a C++ game engine that handles many tasks.
An open source skateboard games engine written in C# and .NET.
An extensible development framework for roleplay games.
C++ SDL/Box2d Programming
A cross-platform Java 2D graphics library using OpenGL.