https://www.hpi.uni-potsdam.de/hirschfeld/trac/SqueakCommunityProjects/wiki/... This has a GUI prototyping tool which is very nice.

http://scratch.mit.edu/ Scratch has in my opinion the best Morphic interface I've ever seen.

http://info.scratch.mit.edu/Source_Code The dev image is here. It's an old image 2.8, but the do marvelous things with the UI.

Chris