I hope you find this as entertaining as I did. A Cocoa App (with a window, even) but not using Xcode). The App itself is a curiosity---though not so much of one as Amit Singh's even shorter program (see the link for details)---but Matt Gallagher obviously knows his stuff, and I can see it serving as a harness for various simple tests.
Maybe I should make a sidebar populated with blogs like his. Check it out.