GTK+

GTK+ is the widget set used for GNOME applications. Its look and feel was originally derived from Motif. The widget set is designed from the ground up for power and flexibility. For example, buttons can have labels, images, or any combination thereof. Objects can be dynamically queried and modified at runtime. It also includes a theme engine that enables users to change the look and feel of applications using these widgets. At the same time, the GTK+ widget set remains small and efficient.

The GTK+ widget set is entirely free under the Lesser General Public License (LGPL). The LGPL enables developers to use the widget set with proprietary software, as well as free software (the GPL would restrict it to just free software). The widget set also features an extensive set of programming language bindings, including C++, Perl, Python, Pascal, Objective C, Guile, and Ada. Internalization is fully supported, permitting GTK+-based applications to be used with other character sets, such as those in Asian languages. The drag-and-drop functionality supports both Xdnd and Motif protocols, allowing drag-and-drop operations with other widget sets that support these protocols, such as Qt and Motif.