Platinum Arts Sandbox Free 3D Game Maker - Vehicle Simulator Mode
Now you can zoom around in your very own racecar and make tracks! Add bots and paths to create race opponents!
Also be sure to check out http://FunFreeGamesHQ.com because that's where lots of Sandbox maps and projects are going to be posted! Also it features free flash games and tower defense games along with free game downloads!
Sandbox is a 3D game creator and 3D game design tool based on the Cube 2 engine that allows users to quickly and easily create and edit their own worlds in game, even cooperatively. It is free, open source, and easy to use for Kids and Adults.