ZK is an open-source Ajax Web framework that enables rich user interface for Web applications with little programming. Its an event-driven, component-based framework to enable rich user interfaces for Web applications. ZK includes an AJAX-based event-driven engine, a rich set of XUL and XHTML components and a markup language called ZUML (ZK User Interface Markup Language).

With ZK, you represent your application in feature-rich XUL and XHTML components and manipulate them upon events triggered by user's activity, similar to what is done in desktop applications. Unlike most of other AJAX frameworks, as far as ZK is concerned, AJAX is a behind-the-scene technology. The synchronization of component content and the pipelining of events are done automatically by the ZK engine.

Your users get the same engaging interactivity and responsiveness of the desktop application, while your development retains the simplicity of developing desktop applications.

In addition to a simple model and rich components ZK also supports a markup language called ZUML. ZUML, like XHTML, enables developers to design user interfaces without programming.

There are actually hundreds of ajax frameworks used today. Please read the following article if you are interested in choosing the best for yourself.

http://ajaxian.com/archives/choosing-an-ajax-framework


If you directly want to see the available frameworks please visit this page:

http://ajaxpatterns.org/Ajax_Frameworks

But the big trick of ZK framework is that you can write Huge and Complex WEB AJAX application without having to write a line of javascript code. That´s why I love it.
Just Java and JSP.
Really Great Framework!