GMPC is a GTK2 client for Music Player Daemon. I’m not going to talk about Music Player Daemon again, because we covered it when we talked about Sonata (including how to configure Music Player Daemon - MPD).
This time we will talk about GMPC, or Gnome Music Player Client, which is a lightweight client for MPD, extendable through plug-ins: alarm, album view, AWN applet, dynamic playlist, fullscreen info, jamendo, last.fm, libnotify, lirc, lyrdb, lyricsplugin, lyricwiki, magnatune, wikipedia info, taglib (for editing tags) and so on (in the latest version).