Puzzles - if that's your thing

[Retro Cat]

http://projecteuler.net/problems

Some of these are dead hard!

 

[02gf74]

not really puzzles per se, but mathematical problems that have no real use, not for me anyway.

try this: http://www.fantasticcontraption.net/

a puzzle based on physics, no use in the real world other than it is more fun than your mathematical 'puzzles'. note that there is a solution to each of the puzzles that do not use any powered wheels, just gravity.