This application uses L-systems to procedurally generate and render 3D models of plants and other fractal-like structures. L-systems are a parallel rewriting system that use a set of production rules to replace symbols in a string with other symbols, allowing for complex structures to be generated from simple rules.
The space bar will iterate the selected system, and 'r' will reset it to the starting axiom. Changing the system settings will copy the current data to the custom system, where you can modify the rules.
Refer to this paper for more information on the control symbols in the production rules.