RAP is a web development plaform based uppon Eclipse and enabling development in a RCP (Rich Client Platform) manner, SWT being "only" replaced by RWT for Rich Widget Toolkit.
The concepts are really interesting and the architecture clever, based uppon server-side OSGI.
I'm not confident by now on the performances of applications developped with RAP, especially on loading and stress tests. But the basis seems good, and could obviously be improved in the future. Personally I would like to see GWT used instead of/in conjunction with qooxdoo, the js library used to implement RWT on the client side.
Concerning Qooxdoo, it seems that a quite similar project to GWT is available for the framework : QWT for Qooxdoo widget toolkit.