Ultimate++ is a C++ cross-platform rapid application development suite focused on programmers productivity. It includes a set of libraries (GUI, SQL, etc..), and an integrated development environment.
U++ looks like an interesting alternative to qt and wxWidgets as a cross-platform widget toolkit -- it has it's own IDE with graphical form design, etc.
There are are a couple of valuable tricks already in this toolkit:
1) a fix for NUnit (and others) to allow unit testing things which must run in STA mode.
2) a way to make your XAML data binding testable by tracing data binding warnings
Compiled library that adds support for your site visitors to login with their OpenIDs by just dropping an ASP.NET control onto your page. It's that easy. An AJAX-style login control is also included for a slick, streamlined user experience.