SmartClient: The little known uber Javascript framework
Basically SmartClient has everything you need to build a "desktop app in a web app" type of application, complete with automatic data binding & synchronization and all of the main types of controls you'd ever need. Often building a SmartClient app requires just hooking controls up to data sources and letting the framework take it from there. It's LGPL and has been around for almost a decade, so its pretty battle tested. Note that bending it in a direction it doesn't want to go can be a bit painful, but generally we've found that often the problem was just not realizing that what we needed was already there in the framework.
v7.0 RC2 is now available, grab it here:
http://www.smartclient.com/product/download.jsp
There are also GWT bindings, check out SmartGWT. Also see the demos at
http://www.smartclient.com/featureExplorer.jsp