Musicus MPC
Musicus MPD client (musicus-mpc) is a client for the music player daemon MPD (visit the MPD homepage at http://musicpd.org/) which comes in two flavors. There is a GNOME panel applet variant as well as a standalone GTK+ interface variant. The latter is a standalone implementation of the Playlist/Media browser component of the GNOME applet.
The program is implemented in C and GTK+. For communication with MPD the libmpd library is used. The panel applet is using the libpanelapplet library from the GNOME framework.
Work is underway on porting the applet part to GNOME Shell (GNOME 3). Check out the gnome-shell-extension branch if you want to try the shell extension.