VDrift is a cross-platform, open source driving simulation made with drift racing in mind. The driving physics engine was recently re-written from scratch but was inspired and owes much to the Vamos physics engine. It is released under the GNU General Public License (GPL) v2. It is currently available for Linux, FreeBSD, Mac OS X and Windows.
This game is in the early stages of development but is already very playable.

Features
Over 20 tracks, almost 30 cars
Simple networked multiplayer mode (currently disabled, waiting to be rewritten)
Very realistic physics
Mouse/joystick/gamepad/wheel/keyboard support
Fully modeled tracks, scenery and terrain
Several different camera modes
Basic replay system with Skip Forward/Skip Backward
Fully customizable controls
Joystick, mouse and keyboard input filtering
Brake lights
Driver aids: automatic shifting, traction control, anti-lock braking
Experimental force feedback