lambda lambda lambda

Hey /prog/, I found this last night:

(define (foo) (lambda (g) (((lambda (f) (g (lambda (arg) ((f f) arg))))) (lambda (f) (g (lambda (arg) ((f f) arg)))))))

What does it do and how do I use it?

Jesus Christ. That is some fucking ENTERPRISE code right there. In fact I think I saw it in the Windows Vista source code.