Wt (http://witty.sourceforge.net/) is a C++ widget library, which uses Ajax to render changes to the widget tree when available.
API inspired by existing GUI libraries. It targets C++ application developers.
The widget library makes complete abstraction of the underlying technology (JavaScript, HTML, Forms, CGI, Ajax).
Documentation is at http://jose.med.kuleuven.ac.be/wt/doc/index.html.
Open source license (Affero General Public License) by Koen Deforche.