UIzard is an in-browser web application development tool built on various Javascript Framework. You can add and arrange UI components easily by using Drag & Drop in-browser environment. You can also edit JavaScript Code or Html Code on the in-browser environment without operating other editors. You can preview the result of your works immediately.

Link: http://www.uizard.org/

UIzard Opensource Project http://code.google.com/p/uizard/

UIzard Developers http://groups.google.com/group/uizard-dev/