- cells-gtk - cells-gtk is a GTK+ based toolkit that enables a declarative-style description of a GUI
- cl-cffi-gtk - cl-cffi-gtk is a Lisp binding to GTK+ 3 which is a library for creating graphical user interfaces
- cl-gtk - Gilbert Baumann's GTK bindings for Common Lisp (for CMUCL, CLISP and Allegro CL)
- cl-gtk2 - CL-GTK2 is a Common Lisp GUI library that provides access to the Gtk+ cross-platform GUI library in idiomatic Lisp style
- clg - Espen Johnsen's GTK bindings for CMUCL, SBCL and CLISP
- Common Lisp GTK-Server Wrapper - Common Lisp Gtk-Server Wrapper is a new way to write platform-independent gui applications in Common Lisp
- gtk-cffi - GTK-CFFI is a Common Lisp GUI library, that provides concise and idiomatic syntax to use GTK+ library (for now GTK+ 3.0)
- lambda-gtk - Lambda-GTK is an apparently complete set of GTK+2 bindings, autogenerated by FFIGEN
- lgtk - Lgtk is Common Lisp GTK binding; not available for CLISP
A few comments by JCh:
- cl-gtk2 seems to be latest and active as of Sept 2009.
- clg is possibly the nicest of the lot. It's complete (autogenerated) and very lisp-ish (GTK classes are represented as instances of a subclass of standard-class, you just make-instance them); unfortunately, it currently only works with recent versions of CMUCL and SBCL;
- lambda-gtk is complete (autogenerated), but not very lispish; GTK objects are just untyped alien pointers (the Lisp incarnation of C's void*);
- lgtk is lispish enough, but incomplete (it's hand-written);
- I haven't looked at cl-gtk.
Another note: Clozure CL ships with gtk2 support in the form of a simple autogenerated binding (through the same ffi interface used for all native Clozure bindings). It's not lispy at all, but it works (you might want/have to re-run the binding generation script though). It should also bring in support for cairo, pango, etc.