a game programming library for C/C++ developers distributed freely, supporting the following platforms: DOS, Unix (Linux, FreeBSD, Irix, Solaris, Darwin), Windows, QNX, BeOS and MacOS X. It provides many functions for graphics, sounds, player input, etc..
a library of functions for 2D graphics supporting a superset of the PostScript imaging model, designed to be integrated with graphics, artwork, and illustration programs.
a free / freeware open source tool for 2-D game development. It is designed for the Windows 9x/DirectX platform, and targeted at people spanning a range of skill levels.