Mutter is a window and compositing manager that displays and manages
your desktop via OpenGL. Mutter combines a sophisticated display engine
using the Clutter toolkit with solid window-management logic inherited
from the Metacity window manager.
While Mutter can be used stand-alone, it is primarily intended to be
used as the display core of a larger system such as GNOME Shell. For
this reason, Mutter is very extensible via plugins, which are used both
to add fancy visual effects and to rework the window management
behaviors to meet the needs of the environment.