Phun is an incredible 2D physics engine in which you can create almost anything: cannons, machine guns, water systems, cars/trucks, Rube Goldburg machines, levers, catapults, springs, and much, much more! Check it out at http://phun.cs.umu.se/wiki/Phun!
PSPPC GameMaker!! Where you can find PSP and PC games up for download!