Unity (and GNOME Shell for that matter) is probably best described as a "shell" rather than a window manager. Like the old school GNOME Panel (and taskbar in W

Unity (and GNOME Shell for that matter) is probably best described as a "shell" rather than a window manager. Like the old school GNOME Panel (and taskbar in Windows, Dock in OS X), the shell is for launching things, the entry point to getting your computer to do things. Both Unity and GNOME Shell rely on an external window manager, albeit in an interesting way: They are plugins for mutter (a Clutter-based version of Metacity). When Unity switches to Compiz, it may be as a plugin or as a separate processs, not sure.