Have two minutes? Give the Lambda Calculus a shot right now!
If you're a beginner you can start with some basics:
(\x.\y.x) z q
(\x.x x) (\y.y y)
Hacked out in a night by Mike Burns. Thanks to Try Ruby and Try Haskell; and to jison and jquery-console. Learn more about the Lambda Calculus at Wikipedia. Fork the source on Github.