For those of you that have never heard of LINE RIDER and think this sample looks like it just may be for kids, I suggest you give it a go. Originally developed by by Boštjan Čadež, a Slovenian university student, this program is based on the laws of physics. It was featured in Time Magazine and Yahoo, and was 2006 Internet Best Toy. Once it hit the web on deviant art, it became a an instant hit.
It is highly addictive, I may add.