Oolite is a space sim game, inspired by Elite, powered by Objective-C and OpenGL, and designed as a small game that is easy for users to pick up, modify and expand upon. Almost every aspect of the game can be changed by using simple, free graphics packages and text editors.
Originally written for Mac OS X, and under continuous development for over five years, Oolite is available for Mac OS X (10.3.9 and higher) and PCs running Windows XP, Windows Vista or Linux. It requires at least a 400 MHz processor, 256 MiB of memory, and a graphics card capable of accelerating OpenGL graphics. The game and source code are offered for free under the GNU General Public License.
Source: The Publisher Website.