CLORB is licensed under the Lesser GNU Public license (LGPL).
CLORB now (since version 0.5) supports valuetype and has an IDL compiler and a code generator to generate stubs (proxy) and skeletons (servant).
A slightly out-of-date guide to using CLORB with GNOME can be found at http://www.pvv.ntnu.no/~ljosa/doc/encycmuclopedia/devenv/gnome-lisp.html. Note in particular that the patch linked to on that page is no longer needed: it was rolled into CLORB 0.1
There is a 'orbit.lisp' file included that you need to load to talk to Gnome.