GTK, which stands for the Gimp ToolKit, is a library for creating graphical user interfaces. It is designed to be small and efficient, but still flexible enough to allow the programmer freedom in the interfaces created. GTK provides some unique features over standard widget libraries.

GTK is primarily used for creating Gnome applications however GDK has been ported to Windows and MAC. You can now effectively create cross-platform applications for Windows, MAC and Linux using GDK. There is currently no Visual Studio like IDE for GDK making it fairly difficult to program for. There are a few IDE attempts but fail because of difficulty and compatibility issues. GTK is still one of the most widely used GUI libraries for Linux.

There are downloads for Windows, Linux and MAC on their website.