Thanks to kvl's Audatorium thread I was hooked at it for more than a few hours and thanks to the game being unfinished I now have my life back. The last time this happened was at this site,

http://fantasticcontraption.com/

Ok 'online physics puzzle game' does it no favours in the advertising department. In order to solve problems you build things, wild things, crazy things, broken things. Probably the biggest strength of this game though is just how many completely different ways there are to solve every level. I've spent more than 2 days stuck on a level and when I've finally figured out a solution it turns out to be nothing like anyone elses....

It is a great game, but it's really short and sometimes you can use the same contraption to beat it.

However, I too have spent many hours, when I was in school, building different contraptions.