"Modifications" are defined as files that replace game content rather than adding on to it. New code is generally a mod (SuperTux isn't extensible yet), as well as most sounds, but most levels and graphics are just contributions.
Christoph's Forest 2
Christoph's Forest 2 is a tileset modification for SuperTux 0.1.3. It features a subset of the new "Forest Theme" tiles from the upcoming milestone 2 release as well as some new "Dark Snow on Ice" tiles.
Note that these tiles, levels to use them, new added features, and more are already available in the unstable package.
This is a patch for running the game on systems without OpenGL support. Also in the unstable package.
SuperTux Cheat Mod
A modified version of SuperTux with built-in cheats. (Download links broken)
A game made to look like a "3D mod" of SuperTux. Under Development.
Supertux 0.1.3 world2
Theres also a mod called: world2. Includes 18 levels to play, plus 32 secret levels. In the new island, theres a total of 22 levels, on the secret worldmap, theres 32 levels. If you found the secret worldmap, there´s a little surprise on the final level.
Also, look to the mods collection by MegaGTA4Master:
Supertux 0.1.3. 6-in-8 island
New mod by MegaGta4Master arrived!
Go to his youtube channel:
Also watch the video about the mod:
Creating and Playing Mods