Spring is a free RTS engine developed for Windows, Linux and Mac OS X.
Free and Open Game Programming Language for Windows and GNU/Linux
The Old PacMan! programed over the Salvat Game Fabric platform
Cross-platform C framework very compact libraries and tools.
C++ Framework for slot machine games
Investigo - DX9 Performance and Debugging Toolkit
A C++ library for programmers transitioning from "Game Maker Language"