There are now screenshots up of the GTK# interface for WarFoundry. The GUI is mainly aimed at Linux users, since GTK is what powers to Gnome desktop on Linux, but there are also ports to Windows.
The underlying code that powers the back-end is still the same API as was used in the older System.Windows.Forms screenshots (native MS Windows), even if it has been greatly overhauled. From a developer's point of view, though, it shows that you can easily attach two different GUIs to the same API and that the API is nicely separate from the GUI implementation.