Racer is a free cross-platform car simulation project (for non-commercial use), using professional car physics to achieve a realistic feeling and an excellent render engine for graphical realism.
Cars, tracks and such can be created relatively easy (compared to other, more closed, driving simulations).
The 3D, physics and other file formats are documented.
Editors and support programs are also available to get a very customizable and expandable simulator.
OpenGL is used for rendering.
Download from the Racer website here... http://www.racer.nl/
Source: Free Online Fun