I made an open source project last year called Mockdown that does the opposite of PaintCode. It takes declarative design code and converts it to PNGs so they can be used in iOS apps. The original idea was to do mockups but it actually turned out to be more interesting as an open source design tool.

Here's a short 5 minute walkthrough in designing the Mail app in Mockdown:

http://vimeo.com/23869680