gtkmm (previously known as Gtk--) is the official C++ interface for the
popular GUI library GTK+. Highlights include typesafe callbacks, widgets
extensible via inheritance and a comprehensive set of widget classes that
can be freely combined to quickly create complex user interfaces. Here's
an overview, with documentation and status. gtkmm is free software
distributed under the GNU Library General Public License (LGPL).

Aside from the C++ interface to Gtk 2.x, this package also provides
bindings for glib, atk and pango (all of them related with the toolkit).