PhoneGap: A free and open source framework that allows you to create mobile apps using HTML, CSS and JavaScript.
Titanium: An open, extensible development platform for creating beautiful native apps across different mobile devices and OSs including iOS, Android, Windows and BlackBerry, as well as hybrid and HTML5.
jQuery Mobile: A unified, HTML5-based user interface system for all popular mobile device platforms, built on the rock-solid jQuery and jQuery UI foundation.