In this lab, you can observe Diffusion-limited aggregation. DLA is a process in which particles of matter come together (aggregate) while they randomly move (diffuse) through a medium that provides some sort of resistive (limiting) force. You can observe that as the particles clump together over time they form characteristic fractal branching structures (Brownian Trees). 

You can modify the degree of attraction to the centre, the number of dots (particles), and its radius. Also, try changing the colours to get a different view of the formation of these structures.