which used GTK for rendering. "Mutter" is a combination of "Metacity" and "Clutter". Mutter can function as a standalone window manager for GNOME-like desktops
Mutter. The Pantheon desktop environment is built on top of the GNOME software base, i.e. GTK, GDK, Cairo, GLib, (including GObject and GIO), GVfs, Vala
desktop environment to a custom-built GNOME Mobile UI based on OpenedHand's Clutter, a key piece of the Maemo graphical environment, built around the X Window