Lambda-GTK is an apparently complete set of GTK+2 bindings, autogenerated by FFIGEN. From the website:

λgtk is a cross-platform Lisp interface to the complete GTK+2 family of shared libraries. λgtk currently runs in the following Lisp environments:

and is released under the Lisp Lesser General Public License (LLGPL).

If you are familiar with Lisp function call syntax and the GTK API then programming with λgtk is straightforward. See examples.lisp for some demonstrations translated from the GTK tutorial.

It was generously released by Rick Taube, using Gary Byers' ffigen.

The website is at

GTK binding, GUI