TORCS is an open source 3D racing simulator using OpenGL technologies.
It is runnable on all Linux, FreeBSD, MacOSX and Windows platforms.
There are 50 different cars, 20 tracks and 50 opponents to race against.
The multiplayer mode can accommodate up to 4 human players. Several of the simulation include damaged models, collisions and aerodynamics like ground effects, spoilers, etc.
Development is currently being carried out to enable online racing mode.
Download here... http://torcs.sourceforge.net/
Source: Free Online Fun