Use Spacebrew to generate a forest of trees! We set up a physical button, an arduino, and a processing sketch to send events to Spacebrew, and another computer to use those events to draw a forest. See here for the project in action:
http://vine.co/v/b6mzJvXaU7A

single_tree.pde generates a different tree on mouse click
forest.pde generates a different forest of trees on mouse click
spacebrew_forest.pde adds a new tree when pressing a physical button.

Written with Processing & Spacebrew. Tree-drawing code based on this OpenProcessing sketch:

http://www.openprocessing.org/sketch/1249

http://docs.spacebrew.cc