This is a fun applet for students to see recursion in action. This project can be seen in the Apple Store for free download on iPhone/iPod. All of the code is written and you can delete out the recursive method. Easily modified to see drawing effects before or after the recursive call.
See PythagorasTree in the Apple App store https://itunes.apple.com/gb/app/pythagorastree/id421785224?mt=8