[flavoie]

You can also take a look at qooxdoo. http://qooxdoo.org/

It's feature rich (more than cappuccino at this time), it has good documentation, it provides a nice unit test framework and it's easy to use.

One thing that worth noting, is that framework like capp/sproutcore/qooxdoo are design with all the widget in mind(not the case with jQuery). That provide a more coherent api, everything is test against each other, it's easier to build, maintain and update. But all of this at the expense of being a little bit bigger (kb).

One advantage of cappuccino is the GUI builder Atlas, but only if you're on a Mac and all your team members are on a Mac. There is no announcement yet if or when it will be available on Windows and Linux.