GWT (Google Web Toolkit), an open source Java software development framework from Google has been released as an Open Source Project. It's under license of Apache 2.0.
Here are some features from GWT (taken from GWT's official web page):
* Dynamic, reusable UI components
* Really simple RPC
* Browser history management
* Real debugging
* Browser compatible
* JUnit integration
* Interoperability and fine-grained control
* Completely Open Source
With the introduction of Java 6 which includes scripting features, i think this two apps will be a great combination in the future. You can use Java as the front-end application and use scripting languages to dynamically update your application real-time.