Physica

Physica is a casual platformer game where the goal is to drive a square through game levels from its starting position to his goal, avoiding hazards and without falling down.

The 2.0 release includes 2 packs of 16 levels each, plus a level editor to make your own ones.

There's also a Portable Apps Format release (still in beta testing: see http://portableapps.com/node/36645 for corresponding thread):
http://sourceforge.net/projects/physica/files/PhysicaPortable_1.0.paf.exe/download

Check out the game website at physica.sourceforge.net

You can also find the repository with game source code here: https://github.com/buch415/Physica

All graphics are released under CC-BY license and can be found here:
http://opengameart.org/content/physica-assets-0