Racer is a free car simulator project, using high-end 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 files, physics, and different Racer-specific file formats are documented. Editors and support programs are also available to get a very customizable and expandable simulator. OpenGL is used for rendering.
Editor's Note:
Many more cars and tracks can be downloaded at the authors site.