Steve's Portable Game Libraries
PLIB includes sound effects, music, a complete 3D engine, font rendering, a simple Windowing library, a game scripting language, a GUI, networking, 3D math library and a collection of handy utility functions. All are 100% portable across nearly all modern computing platforms. What's more, it's all available on line - and completely free. Each library component is fairly independent of the others - so if you want to use SDL, GTK, GLUT, or FLTK instead of PLIB's 'PW' windowing library, you can.