"ZK is an open source Web development framework that enables Web applications to have both rich user experiences and low development cost as you did for years in desktop applications. ZK includes an Ajax-based event-driven engine, rich sets of XUL and XHTML components, and a markup language.
* The event-driven engine brings the intuitive desktop programming model to Web developers.
* The XUL and XHTML components enrich Web applications by off-the-shelf building blocks.
* The markup language, called ZUML, makes the design of rich user interfaces as simple as authoring HTML pages."