GtkAda

Download: GUI Router for GtkAda (.zip 11 KB)
Download: Using GtkAda in Practice (Article printed in AUJ 38-3) (.pdf 783 KB)

GtkAda by itself is not very easy to use.
At the very least it needs a server mechanism to execute the GtkAda code on behalf of the GUI.
Gui-Router is a working example of such a server.