Comment Qooxdoo (Score 3, Informative) 147
I've tried Dojo and the Prototype derivatives - Moofx, Rico and Scriptaculous. I don't really like Dojo because it seems so basic. Moofx is pretty good for lightweight effects, and the weight factor for effects goes up with Rico and even more with Scriptaculous. Bad thing about Prototype based scripts is that it doesn't play well with others due to Prototype's large manipulation of core objects.
Enter QOOXDOO. Qooxdoo surprised me with how advanced it was. And its free. It is definately the script anyone needs to build a complex user interface for any application, because its designed to look just like an application.
Its documentation is sparse, but the development community is amazing. they respond very quickly, and are working hard to fill the gaps on the documentation. The latest version is a vast improvement. The examples are very diverse, showing all the possibilities this remarkable script can do.
if you really want to see an advanced framework that looks incredibly awesome, check out Qooxdoo...http://www.qooxdoo.org