To download SuperTux, you can choose between two types of packages and the development repository:
The stable release contains a playable SuperTux that should not suffer from critical bugs and has had much testing. If you simply want to play the game this is the package for you.
The development snapshot contains a playable SuperTux that has not been fully tested and may suffer from critical bugs, but does sport newly added features. This package is for showing off and testing new features and levels, so don't expect it to be good, fun, well-balanced game. Be warned that it may not work well on your system, if at all. If you simply want to play the game use the stable package instead; if you are a SuperTux expert and want to experiment with the new features, you might want to try this version. Package managers and repositories should not include this package unless it is slotted beside the stable version.
The Git repository (formerly the Subversion repository) contains SuperTux in a state of development. This means new features and a large amount of bugs. If you are interested in the development of SuperTux, feel like contributing or just simply want to try out the new features and you are ready to endure some bugs and crashes, this is what you want. If you have never played SuperTux before and are interested in developing SuperTux, it is recommended you try out the stable package first.
Links to additional game content can be found on the following pages:
The level editor for SuperTux 0.3 can be found in the same Git repository as SuperTux itself.
The Editor 0.3.2-SVN snapshots contain start-able SuperTux-editor binaries that may suffer from critical bugs since only basic tests were performed, but have a lot of new features. They are for all users who do not want to compile the editor and won't be annoyed if error/level data loss occurs. They can be used with any 0.3.x game, but only 0.3.1 will be recognized automatically. Be warned that it may not work well on your system, if at all. Be also warned that there is a small amount of features from Subversion that aren't supported in 0.3.1 or 0.3.0. Package managers and repositories should not package content of these archives unless it is slotted beside the stable version.
Additional to the built-in editor of SuperTux 0.1 there is also the Flexlay editor which provides more features and better level editing capabilities. You can find it at
https://github.com/Grumbel/flexlay
You can find older releases here:
http://sourceforge.net/project/showfiles.php?group_id=69183
and here:
https://github.com/SuperTux/downloads/
There are lots more unofficial ports of SuperTux for various platforms.
These are collected at Download/Portable.