Jigloo
Jigloo creates and manages code for all the parts of Swing or SWT GUIs as well as code to handle events, and shows you the GUIs as they are being built. Jigloo parses java class files to construct the form that you use when designing your GUI (round-tripping), so it can work on classes that were generated by other GUI builders or IDEs, or hand-coded classes. It can also convert from a Swing GUI to a SWT GUI and vice-versa. Jigloo GUI Builder is a plugin for the Eclipse Java IDE and WebSphere Studio, which allows you to build and manage both Swing and SWT GUI classes.
