This is what I’ve been wasting my time with…

http://www.captainforever.com/captainforever.php

and this

http://magic.pen.fizzlebot.com/

Magic pen is the poor man’s “Crayon Physics”, which, if you have a PC I recommend you check out (there is a free demo at http://store.steampowered.com/, and while you’re there you should also download the demo for “World of Goo”).