sentences:  It has been replaced in GNOME 3.x by default with GNOME Shell, which only works with the Mutter window manager.There are many "applets" for GNOME Panel available in one package called "gnome-applets" while some applets included with GNOME Panel as built-in, like a traditional start menu.GNOME Panel served as Fallback Mode until GNOME 3.8 when Mutter could not be executed, then it was replaced with a suite of officially supported GNOME Shell extensions named GNOME Classic.