The Liquid Webtoy is an interesting fluid simulation made by DAN-BALL. It is similar to the falling sand games, but it uses round particles instead of one-pixel particles, as well as having more liquids. You can change the background, if the elements have outlines, etc. There are many different elements:
Water: Basic element. Sloshes around.
Paint: Changes the color of water. You need Hit turned on to use this.
Cloud: A cloud, which when it hits the ceiling, turns into water. Also carries ducks.
Magma: Makes ducks red, and turns water into cloud.
Ice: Makes ducks blue, and freezes water.
Wall: Blocks other elements, and serves as a platform.
Bomb: Pushes other elements away.
TBomb: A timed bomb.
Duck: Your poor test subjects. Please, think of the ducks!
Clear: Erases wall.
Black Hole: Pulls in all elements except wall.