GTK+ is a multi-platform open source GUI Toolkit. Everything about GTK+ from the object-oriented design to the Free Software LGPL licensing allows you to code your project with the most freedom possible. You can develop open software, free software, or even commercial non-free software without having to spend a dime for licenses or royalties.
GTK+ is a set of libraries to create graphical user interfaces. It works on many Unix-like platforms, and a Windows version is in development. GTK+ is released under the GNU Library General Public License (GNU LGPL), which allows for flexible licensing of client applications. GTK+ has a C-based object-oriented architecture that allows for maximum flexibility. Bindings for other languages have been written, including C++, Objective-C, Guile/Scheme, Perl, Python, TOM, Ada95, Free Pascal, and Eiffel.
GTK+ consists of the following component libraries:
Provides many useful data types, macros, type conversions, string utilities and a lexical scanner. Includes Win32 support.
A wrapper for low-level windowing functions.
An advanced widget set.