SuperTuxKart is a free 3D kart racing game. It aims towards fun for players of all skill levels, with item boxes giving random items, nitro, drifting and more. Realism is not the focus.
STK offers an online multiplayer mode, a local multiplayer mode, and a single player mode against AIs with both custom races and a story mode to complete to unlock new karts and tracks. It features Grand Prix where the goal is to get the most points over several races.
Its 21 tracks will take you in varied environments. From the beaches of sunny islands to the depth of an old mine, from the streets of Candela City to peaceful countryside roads, from a spaceship to the mountains, you have much to explore and discover.
The game also features additional game modes besides normal races : time trials, follow-the-leader, soccer, capture-the-flag and two types of battle mode.
Source: https://supertuxkart.net/FAQ