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.