What is "metacity"

Metacity was the default window manager used by the GNOME 2 desktop environment until it was replaced by Mutter in GNOME 3. It is still used by GNOME Flashback, a session for GNOME 3 that provides a similar user experience to the Gnome 2.x series sessions.

A fork, Marco, is still being actively developed and maintained as part of the MATE desktop environment, itself a fork of GNOME 2 as a whole.

The development of Metacity was started by Havoc Pennington and it was released under the GNU General Public License. Before the introduction of Metacity in GNOME 2.2, GNOME used Enlightenment and then Sawfish as its window manager. Although Metacity was designed to integrate into the GNOME desktop, it does not require it to run, while GNOME can be used with different window managers provided that they support the part of the ICCCM specification that GNOME requires.

Metacity uses the GTK+ graphical widget toolkit to create its user interface components, which makes it themeable and makes it blend in with other GTK+ applications. Originally, Metacity used GTK+ 2 however as of version 3.12.0 it has been ported to GTK+ 3.