The Vaadin framework is a server side programming model for web based GUI. It is for developers, architects who prefer to avoif programming using frameworks like jQuery, JSP, JSF. Also, output generated by Vaadin is compatible across web browsers including mobile / handheld devices.
The Vaadin framework programming is carried out in Java as kind of SWING library. The same is compiled into .classes using Java compiler. However, at runtime, the framework is available in a Jar file which has to be included in WAR file. The WAR file takes care of generating appropriate HTML / DHTML and AJAX scripts which is sent to web browser for display. So all browser compatibility issues are taken care by vaadin framework.
Also, vaadin has a plugin for Eclipse which makes development so much easier including drag-n-drop support for UI widgets.
Vaadin is open source project with very good community support including forums.You can check out vaadin at - Vaadin Homepage
I played around with vaadin using vaadin documentation which is very exhaustive, and found it simple to use and develop.