Pow is a Node.js app written in CoffeeScript. It includes an HTTP and a DNS server and runs Rack apps by way of Josh Peek's Nack library: https://github.com/josh/nack

The screencast shows how it works and why we made it: http://get.pow.cx/media/screencast.mov

If you're interested, you can read the annotated source code, written in literate style and generated with the wonderful Docco: http://pow.cx/docs/