Top-down open-source racing? Yorg is a little bit like some of the classic Micro Machines games and while rough around the edges as it's in development it's showing promise as another FOSS game.
With fast arcade racing along with some amusing physics, Yorg is already a lot of fun with multiple tracks, vehicles and different drivers to pick from. You can play against AI, local multiplayer and experimental online multiplayer. There's weapons too, so you can blow everyone up.
The latest release Yorg 0.11.1 expands the gamepad input support, cleans up the UI somewhat and the camera should feel a lot better during races. Plenty of bug fixes went into this release to improve the AI, reduce CPU usage, improve the audio and multiplayer and so on.
Hopefully more players and developers will pick it up, we can always use more good free and open source games.