Phun, well, is a fun game. It is a sandbox physics game that you can do pretty much anything in. For example make a bar with a hinge in the middle and it attached to the background, then draw a ball on one end, and another (bigger) one a little ways above the other. After that, simply press play and watch your masterpiece in motion.
In this game you can do many things like make a shape of your own, a square or rectangle, circles, chains, infinate plains, springs, tracers, gears, and lots more, especially if you buy the full version! And if you get really creative, you can built robotic arms, guns, neat-o explosions, and many others. the possiblities are seriously, endless!
To download this game go to http://www.phunland.com/wiki/Download it is only about 5MB and will run ok on most computers.
This game you can play for hours because of all the possibilities, so that said, I would recommend this game to anyone that has a basic understanding of physics.