What I'm looking for is a type of user interface that has various generic elements which can be edited and arranged in a WYSIWYG manner by the user. Various backend models can be plugged in, and the user can then edit layouts of buttons, sliders, textual or graphic display elements, etc., and hook them up to control and display aspects of the chosen model(s).
The only system I've found so far that resembles what I have in mind is Morphic in Squeak Smalltalk. Are there any similar systems for any other languages or environments?