Ha55ii, creator of the previously reviewed Liquid Webtoy, has put forth another addictive webtoy: Powder Game. It bears a similarity in essence to the World of Falling Sand games, but takes it a step further with the introduction of wind and air pressure.
Most of your favorite elements from the World of Sand are present here, with a couple of new ones, too. Powder, water, and fire are pretty self-explanatory. Seed will grow a little shoot if brought in contact with powder (curiously, water is not necessary). Gunpowder will cause an explosion if contacted by fire. Ice does not get blown around, and water will turn to ice when it touches existing ice. Fire melts ice.
What's really cool are the wind and fan elements. Placing wind causes a temporary breeze to blow around, and placing fan causes the same effect except permanently. These winds blow around and around, spiraling hither and yon and causing a lot of chaotic feedback. You can add wheels that act like windmills and turn in the direction of the prevailing wind.
What I find most fascinating is that the winds are actually modeled by creating a difference in air pressure: low pressure shows up blue in the background and high pressure shows up green. This creates some beautiful shifting aurora-like patterns; static images do not do this game justice. Air pressure is also affected when gunpowder explodes, meaning that you can actually make a chamber that is pressurized relative to the rest of the screen by setting off some gunpowder in a sealed chamber of block.
Another neat idea is to create a system of fans, water, and ice. High winds cause the ice to turn to snow, but the winds also blow the water into the ice. It's fun to just watch the two competing forces go at it, freezing and unfreezing, making icicles and melting them. And every once in a while, igniting some gunpowder to shake things up!
I'm sure there are many more fascinating systems just waiting to be discovered. So what are you waiting for?
While you're over at dan-ball.jp, check out a couple of ha55ii's other toys: Compasses and Planet simulation. Both are good for brief diversions, but probably won't keep you interested for more than 10 minutes.
Note: These webtoys are Java applets, and therefore require a working Java runtime environment on your computer. You may download the latest Java free using the 'get Java' button in the sidebar.