SRB2 kart is a Mario kart like mod on the doom engine, using Sonic characters and themes. There are plenty of custom characters and tracks loaded on the server, so you don't have to like sonic to enjoy it. Enter the race, and change your character, through the start menu when in the server.
The game has been updated to 1.0.4, please update your client if you've played before. Addons can be downloaded automatically when joining the server, but it's recommended you download and extract this pack into your addons folder.