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