"Thematic is a free, open-source, highly extensible, search-engine optimized WordPress Theme Framework featuring 13 widget-ready areas, grid-based layout samples, styling for popular plugins, and a whole community behind it. It's perfect for beginner bloggers and WordPress development professionals..."

http://themeshaper.com/thematic/

This doesn't really have anything to do with mobile development directly, but I'm sure there's a way to make a mobile theme out of this framework. I just came it across it today and thought it was pretty cool. Enjoy!