Glade is a visual user interface designer for the GTK+ toolkit and the GNOME desktop environment.
User interface description files are saved as GtkBuilder XML files, which can then be easily loaded into a GTK+ app written in C, C++, C#, Vala, Java, Perl, Python, and others.
Although primary used on Linux, binaries are also available for Windows and Mac, and GTK+ apps developed with Glade can be written to run unmodified on Linux, Windows, and Mac.
Glade is Free Software released under the GNU GPL License