Flow

An ASCII-based fluid dynamics simulator. Strangely mesmerizing.

EDIT: After playing around with this for a few minutes, (which is quite relaxing, by the way), I am reminded of a toy from my childhood. While the name escapes me, those of you who grew up in the Seventies may remember it. It was a round, flat piece of plastic, with a surface on the front that was essentially two pieces of semi-soft plastic sheeting with liquid crystal sandwiched in-between them. You used your finger to push the liquid crystal around, and it changed colors due to density alteration and the heat from your finger. As I said, I can't remember the name, but I can clearly see it in my minds eye, and this software toy reminds me of it.