GTK+ is a multi-platform toolkit for creating
graphical user interfaces (GUIs). GTK+ is suitable for projects ranging from small one-off projects to complete
application suites. GTK+ is free software and part of the
GNU Project.
However, the licensing terms for GTK+, the GNU LGPL, allow it to be used by all
developers, including those developing proprietary software, without any license
fees or royalties. [Source GTK+ Web site]
GTK+ - The GIMP Toolkit GTK+ is a multi-platform toolkit for creating graphical user interfaces. Offering a complete set of widgets, GTK+ is suitable for projects ranging from small one-off projects to complete application suites.