SimPhy!

Algodoo, previously Phun, is an educational, entertaining and somewhat addictive piece of software for playing around in a 2D physics sandbox in a cartoon-y fashion. Algodoo is not just another game, but is intended to bring in interactive physics as an enabling technology for entirely new concepts and usage patterns in creative computing for animation, simulation, narrative-y, engineering, art and education.

Physion is a Physics simulation software for creating interactive physics simulations and educational experiments.