1. The GIMP Tool Kit is a set of widgets for the X11 windows system originally made for GIMP; the GNU Image Manipulation Program. From Linux Guide @FirstLinux

2. At one point, before KDE was substantially complete, Qt antagonists reasoned that since there were more lines of Qt code than of KDE code, it would be better to develop a widget library from scratch--but that is an aside. The Gtk widget library was written especially for gimp (GNU Image Manipulation Program), is GPL'd and written entirely in C in low-level X calls (i.e., without the X Toolkit), object oriented, fast, clean, extensible and having a staggering array of features. It comprises Glib, a library meant to extend standard C, providing higher-level functions usually akin only to scripting languages, like hash tables and lists; Gdk, a wrapper around raw X Library to give GNU naming conventions to X, and to give a slightly higher level interface to X; and the Gtk library itself. Using Gtk, the Gnome project began, analogous to KDE, but written entirely in C. From Rute-Users-Guide