jQuery Mobile is a HTML5 based user interface system for all popular mobile device platforms.It built on the rock-solid jQuery and jQuery UI foundation.
jQuery mobile framework takes the “write less, do more” mantra to the next level: Instead of writing unique apps for each mobile device or OS, the jQuery mobile framework allows you to design a single highly-branded web site or application that will work on all popular smartphone, tablet, and desktop platforms.
See the full list here.

jQuery Mobile is super easy to use. If you know basic HTML, you can start building mobile sites right away.
You can use this service to build your mobile device using drag and drop 🙂

Also to learn jQuery Mobile and to get inspired you can visit there nice and organized Resources area.