If anyone said, what is the closest game you can find to the falling sand game I would have to say this one.

"Water - As simple as it comes, spray water on the screen and watch it slosh around.
Paint - Mix your own color and meld it with the on-screen liquid.
Cloud - Gloopy clouds float to the top of the screen and fall when they get too dense.
Magma - The mostly-stationary magma turns water to steam (which acts like Cloud) when it comes in contact. Use it to create some interesting feedback loops.
Wall - Create sections to perform different water experiments on.
Bomb - Need I say more?
Duck - Rubber ducky, you're the one. Floats on top of the water and resists even the hottest magma (try that in your bathtub!)
BH (Black Hole) - Suck up all the matter surrounding your cursor. Way too fun."

[via Jay is Games]