Oolite

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 four years, Oolite is available for Mac OS X (10.3.9 and higher), Windows XP and Vista, and Linux. It requires at least a 400 MHz processor, 256 MiB of memory, and a graphics card capable of accelerating OpenGL graphics.

Free Full PC Game Download (v1.65 - 18 MB):
Official link