This fast and versatile library was used all over the world for all
GNOME applications, the GIMP, and several others. Originally it was
written for the GIMP and hence has the name GIMP ToolKit. Many people
like it because it is small, efficient, and very configurable.

Most applications which used GTK1 have since switched to gtk2 (GTK2).
Besides a more flexible API, it provides improved text rendering using
pango (Pango) and many other goodies, but GTK+ 2 lacks compatibility
with GTK1, so to switch, programmers have to port applications to it.

Thus, some applications for which GTK1 is sufficient, still to use
GTK1. GTK1 remains faster and less complex than GTK2. To develop
applications with gtk, you need the package gtk-devel.