Remember my post Crap code of the moment: libgip (and how to make it better)? I implemented most of things I listed in my post, did some tutorials and documentation.
After that post I started to wonder how difficult was to code a basic prototype and I thought it was easy, so in about 4 hours I coded a basic abstraction using Python and GTK+2. It was just a GtkWindow with 5 areas (combination of GtkHBox and GtkVBox) and a few widgets.
Then I started to play with it and after writing some documentation and the tutorial I added more interesting stuff. Some required stuff is still missing, like a "grid" (a.k.a. GtkTextView, QListView, ...), automatic thread support, menu and toolbars.
Now it's reasonable mature and has even an entry at Python Package Index: http://www.python.org/pypi/eagle/ and also a home page at http://www.gustavobarbieri.com.br/eagle/. Code repository is at http://code.gustavobarbieri.com.br/eagle (it uses SVN).
Remember: Ealge is not meant to be "yet another" toolkit, instead it build atop existing toolkits adding features and some restrictions to help you to develop your applications. Narrowing the scope of what can be done with this library, things could be made easier to its users, like the automatic layout in one of the 5 areas and the label at right of user entry components.