syfluid
Fancy interactive fluid simulation for gfx fans, VJs and demo coders
syfluid is a funny toy as well as a real simulation. It simulates a fluid or a gas in a very colorful, graphic and sometimes psychodelic way. In realtime!
Drag while your right mouse button is pressed to "draw" the fluid/density field. Drag while your left mouse button is pressed to make the whole thing move, i.e. to "draw" the "forces" that you're adding to the fluid/density field.