wxCode project is a collection of reusable components based on the cross-platform wxWidgets GUI toolkit. The project provides various tools and facilities for building, maintaining and releasing wxWidgets-based code. Visit the website for more info.
Note: As of January 2018 this project has been retired.
ColGUI is an Open Source distributed web-based GUI builder aimed at increasing designer collaboration on GUI projects. It can read Glade XML layouts and translate them into an interactive DHTML format for lightweight user interactions.
a tool-kit for creating "web 2.5 generation", include several useful stuff to work with semantic web (otology editor, gui for sparql query, ontology components...) and design RIAs's gui visually (html + ajax based apps, flash based apps,...)