jQuery Mobile: Touch-Optimized Web Framework for Smartphones & Tablets
A unified, HTML5-based user interface system for all popular mobile device platforms, built on the rock-solid jQuery and jQuery UI foundation. Its lightweight code is built with progressive enhancement, and has a flexible, easily themeable design.
It is seriously cross-platform with HTML5. It allows you to design a single highly-branded web site or application that will work on all popular smartphone, tablet, and desktop platforms.