Gnome is a desktop GUI for *nix-like systems. It's available both as a package or through ports. Gnome has been designed to appeal to Microsoft Windows users, with menus and icons on the desktop and several GUI interfaces to common operating system and configuration tasks. Its disdavantages stem mostly from a fairly heavy use of resources and underlying complexity. In an office environment, Gnome can be used to completely hide the underlying operating system from a user and in a migration (say from Windows XP) can significantly reduce the level of training needed for users of office applications.
See the website for more info: http://www.gnome.org