Oolite

Oolite is a space-sim game that incorporates trade, battles with pirates, bounty hunting, secret missions and infinitely more. It features high-quality sound and smooth, fast three dimensional graphics, written specifically for Mac OS X using Cocoa and optimised for OpenGL. And it's free. Oolite is written by Giles Williams, who was inspired by the work of David Braben and Ian Bell with Elite, however this work is an entirely independent interpretation and expansion of the original game. Oolite benefits immensely from the creative work of the many people who volunteer their time and skills to test the game, create expansion packs, and suggest and make improvements in this open-source project.