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...