wxCL provides Common Lisp libraries for using the brilliant wxWindows GUI library. Very nice - I have already appreciated wxWindows in its Python incarnation, and in Scheme (via DrScheme) it is also very helpful. Now Common Lispers can use it too. I know that in Common Lisp, of course, CLIM (today often in the form of McCLIM) is the toolkit of choice, especially since it is much more powerful than wxWindows. But still, it's nice to have a cross-platform GUI library, especially because it is available for more than one programming language.