Note: The screenshot is makes this seem duller than it actually is.
Today I wasted my time making a Lorenz Attractor simulation. The Lorenz Attractor is a set of differential equations which can cause some pretty cool looking particle motion; in particular a torus knot.
Updated 2/23/11: I made the applet more interesting by having rho oscillate between 0 and 28 and sigma oscillate between 10 and 20.