Phases of matter
It consists of hundreds of magnetic balls that are weakly attracted to one another, and so tend to stick together. If you add energy to the system by shaking it (heat it up) the balls start to fly around and the clumps evaporate.
As you slow the shaking (cool it down) the particles start to condense out and for droplets or crystals.
The analogy is using very similar physics to the real version so you get deeper behaviours. If you slow it down quickly you form small crystals and if you slow it quickly to form large crystals, just like a real substance.
It is a lovely analogy, and you can spend a long time playing with it.