http://www.fallingsandgame.com/
I've become so addicted to this. You mess with the different stuff (Water, Sand, Salt, Oil, Fire, Wax and Plant) to do whatever. Hell of sand has Zombies, and the downloadable version zxSand has downloadable physics which completely change the game. HOURS OF FUN
some screens:
sounds like something i might be into, however i am concerned with spyware as im using a computer thats probably older than me. i dont have any virus/spyware protection and installing any would only slow down this relic more than it already is. and sorry for rambling.
Use the online version, then. It's Java, so it can't possibly be spyware.
Beware of the online or even offline version if your computer is not fairly powerful. I actually crashed my computer with the java version a few months back when my brother told me about this game.