Luxor is an open-source XML User Interface Language (XUL) toolkit in Java that lets you build UIs using XML and also includes an ultra light-weight, multi-threaded Web server, a portal engine, and a template engine. It is also Web Start-ready, as everything fits in a jar and requires no loose files.
SwiXAT is a Swing-based authoring tool for the quick and easy development of GUI Java applications. It implements a true MVC framework and uses XML to define the view (SwiXML is used as the XUL engine), BeanShell as a scripting language for the controller, and JXPath as the binding mechanism between the view and model. It provides a complete environment in which it is possible to almost write an entire Java Swing application without writing Java compiled code. The use of XPath makes it very simple to traverse the object tree of the application's business model.