It's a free downloadable game for your computer about the speeder bike part of Tron
Find downloads on the side bar and choose which version to download depending on your computer.
It's got online multiplayer, it's customizable, and you can host your own server, all for free. It's a simple game so it has a very quick download and small file size too.
The premise is everyone has a speeder bike. The game is a few years old and was based on the first Tron movie so the bikes move on 90 degree turns (except not on all servers). In the most basic mode, everyone is just trying to kill each other by outmanuevering opponents and forcing opponents to run into a wall. There are other modes such as fortress where you try to capture the enemies base by occupying it while you or your teammates defend your own base. There are a variety of other modes such as capture the flag or races because all the content is user created.
There you have it. It's free downloadable game so try it out if you want.