Are there any good drag&drop web app IDEs out there that support AJAX?

Question

Can anyone recommend a GUI builder tool for creating DHTML web apps using AJAX to communicate with a web service backend? I'd like to avoid having to mess around with designing HTML, marshalling/unmarshalling data, checking for browser compatibility, etc. The tool should have a library of widgets that can be put into an application and hooked up to functionality, and be extensible enough to be able to define custom widgets. Of course free and/or open source is preferrable but I would consider proprietary tools too.

Also to what extent does the choice of GUI tool affect what platform or language I would use for the backend? If the GUI is just calling a web service then I should be able to use anything on the server-side to provide that interface but maybe some gui-side tools use a proprietary data exchange format that requires some specific server-side code?

Edit: I don't need a widget that can be dragged, I want an IDE that allows one to build a gui easily (i.e. a RAD tool).

Answer 1

If you're comfortable with Java, maybe you could try Google Web Toolkit? http://code.google.com/webtoolkit/

Answer 2

WaveMaker is open source, runs on J2EE.