window manager library from the Mutter window manager

 Mutter is a Wayland display server and X11 window manager and
 compositor library. It contains functionality related to, among other
 things, window management, window compositing, focus tracking, workspace
 management, keybindings and monitor configuration.
 .
 Internally it uses a fork of Cogl, a hardware acceleration abstraction
 library used to simplify usage of OpenGL pipelines, as well as a fork
 of Clutter, a scene graph and user interface toolkit.
 .
 This package contains the window manager shared library, used by mutter
 itself, and gnome-shell.