This applet is about chaos and balance. I prefer to let it speak for itself. But I will offer a technical explanation.
400 particles are initialized with random positions and velocities. Around each particle there is a repulsive zone between 30 and 50 pixels from it. Other particles within that repulsive zone are pushed away in proportion to the inverse of their distance from that particle. A global compressive force pushes all particles toward the center in proportion to their distance from the center.