This is Conway's game of life. Cells can be placed with the mouse.
There was a tree simulator here, but I removed it in the transition to a cellular automata approach. Simulating plants is very difficult, yet I just had the idea of a CA where cells store resources (like water) and transfer them out to neighbors with osmosis. If a cell has an abundance of nutrients it could grow a neighbor and if it has a derth it will die. Still need to figure out how to model light and branching.