User Interface Builder for GTK+ and Gnome
Glade is a RAD tool to enable quick & easy development of user interfaces for the GTK+ toolkit and the GNOME desktop environment.
The user interfaces designed in Glade are stored in XML format, enabling easy integration with external tools.
In particular libglade can load the XML files and create the interfaces at runtime.
The DTD for the XML files is included with libglade, and is also at http://glade.gnome.org/glade-2.0.dtd.
Other tools are available which can turn the XML files into source code in languages such as C++, Perl and Python.