FreeGish

FreeGish is a physics simulation platformer where you control a blob of tar. It can slick and slide and jump. There is also a multiplayer with modes like sumo wrestling and football.

Versions
Debian offers a libre version without unfree music for download. The code is under GPL while most media is CC-BY-SA and some textures are MIT and GPL/CC-BY-SA.

The version offered on GitHub uses music under CC-BY-NC-ND 3.0 and CC-BY-NC-SA 3.0 and therefore is not libre.