Green shoes fractal, (from rosettacode.org)

tree.rb

require 'green_shoes'
Shoes.app(:title => "Fractal Tree", :width => 600, :height => 600) do
  background "#000".."#777"
  stroke "#000"
  @deg_to_rad = Math::PI / 180.0
  C=%w{AA0 EE0 FF0 EE0 EE8 EF8 8F8 7F7 0F0 5BB 0FF FAA} 
  def drawTree(x1, y1, angle, depth)
    return if depth <= rand(2)
	s=3+rand(4)
	x2 = x1 + (Math.cos(angle * @deg_to_rad) * depth * s).to_i
	y2 = y1 + (Math.sin(angle * @deg_to_rad) * depth * s).to_i

	stroke "##{C[(C.size-depth)%C.size]}"
	line x1, y1, x2, y2

	drawTree(x2, y2, angle - 10-rand(10), depth - 1)
	drawTree(x2, y2, angle + 10+rand(10), depth - 1)      
  end
 
  drawTree(300,550,-90,12)
end