SuperTuxKart
Or STK for short, is one of the most popular racing games available freely and open-source on Linux. You can find install it in any major distribution with the default package manager. SuperTuxKart comes with several game modes, like single racing or Story mode, vehicles models, inspired by mascots in the free software world (you can drive with Tux, FreeBSD devil, GNU etc) and a whole bunch of maps, which you can unlock by completing missions in the story mode. STK also includes weapons to slow down your opponents. There is an in-game add-on menu from which you can download even further maps and models.