Phun: A physics sandbox you can get lost in for a while

University student Emil Ernerfeldt has written a truly amazing, PC-based physics playground for his Master’s thesis, and it’s free to download and try.

If you’re anything close to my age you probably played Mousetrap when you were a kid. And I don’t know about you, but I hardly ever played the game as it was intended; I set up and played with its Rube-Goldberg marble-track machine instead. Well, this is like that, only you can draw and manipulate any apparatus you can imagine (within the confines of Phun’s 2-D world), quickly and intuitively.
So what can you build today?