GNOME
GNOME is the GNU Object Model Environment, intended to provide a user-friendly "desktop environment" for UNIX operating systems.

Find it at GNOME Home

Components of GNOME are largely licensed under the LGPL, and many of them are libraries written in C. GNOME uses CORBA to access some GNOME components, and uses a CORBA implementation called ORBit.

GNOME has a bunch of language bindings to allow developing applications and components in other languages than C. Although ORBit does not yet support Common Lisp, any IIOP-compatible ORB (eg CLORB) will talk to it. Note also that clg and cl-glade will both allow Common Lisp binding for Glade, the GUI construction tool used with GNOME.

GNOME apps use Gtk for widgets and general graphical stuff

There is a "competing" environment called KDE.