GGv is the Gnome PostScript viewer program. The name comes from GhostView, a non-gnome GNU PostScript viewer application on which GGv is based.
GGv is a frontend for Ghostscript, an interpreter of PostScript that is able to properly render PostScript documents in a display or a printer. GGv serves as a layer that isolates the user from the cumbersome options and interface of Ghostscript, and, at the same time, gives extra features such as panning and persistent user settings.
The main features that make me personally like GGv are its antialiasing (use the preferences dialog to turn it on and reload the document - your eyes will pop out of their sockets so be careful) and nice user interface, allowing e.g. dragging of PostScript files into GGv, moving the PostScript display by dragging the mouse in the pager window or the main window. GGv can display more than one document at the same time. Also, the transparent support for compressed PostScript and pdf are handy.