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.
To tweak this sketch, first download it.
Make your updates, then upload your tweak!