PopsiGames
SuperTuxKart is a free 3D arcade kart racer. Pick a mascot driver, grab power-ups such as bowling balls and plungers, and race through tracks full of shortcuts, ramps and hazards. It is a game to pick up fast and keep playing for the tracks.
There is a story mode with unlockable tracks, Grand Prix cups, time trials, and extra modes such as battle, soccer and capture the flag. Split-screen lets friends share one computer, and online races let you meet other players. Add-on karts and tracks come from the community and install from inside the game.
It is open source under the GPL, built by volunteers, and free of ads and purchases. A gamepad makes it feel best, but the keyboard works well too.