HPInstitute has Morphic Designer, which is interesting but I found a bit
hard to do anything with.

I have used it, and it works well. There are only small glitches when
you try to make scrollbars vertical. But it's worth to extend. And it
has its own set of widgets. The current version has solved the problem
of reinitializing the class. Now it just generates some code inside a
method in a class, so you can modify it easily afterwards.