有什么好的拖放web应用程序ide支持AJAX吗?

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.Can anyone recommend a GUI builder tool for cre