It forms a core part of the GNOME desktop.
It has been replaced in GNOME 3.x by default with GNOME Shell, which only works with the Mutter window manager. GNOME Panel serves as Fallback Mode when Mutter can not be executed, although it can still be activated if a user still wishes to use it as their default desktop.
The gnome-panel module provides:
the panel the libpanel-applet library. This library allows one to develop small applications which may be embedded in the panel. These are called applet. several applets (the Workspace Switcher, the Window List, the Window Selector, the Notification Area, the Clock and the infamous 'Wanda the Fish') (other applets are in GnomeApplets)