Beets is a media library management system designed for obsessive-compulsive music geeks. It catalogs your collection, automatically improving its metadata as it goes using the MusicBrainz database. It also downloads cover art for albums it imports. Then it provides a bouquet of tools for manipulating and accessing your music. Beets also includes a music player that speaks the MPD protocol, so you can play music in your beets library using any MPD client.
MPy3 is a full-featured, modular, configurable MP3 player system aimed at jukeboxes or car MP3 systems. It can play MP3s via rxaudio or mpg123, take input from a keyboard (tty), LIRC, or joystick. It does output through a CrystalFontz LCD directly, or through any LCD that LCDProc supports, or even through X. It features playlist support and support for controlling the mixer (using aumix). All of the inputs, outputs, and other functions are controlled via a number of modular libraries which can be used in other projects as well.
dudl is a collection of tools to grab, encode, and rename MP3 files, archive them, and maintain a database of all files. On top of this runs the dudld Jukebox daemon that plays your files through gstreamer. dudld's strengths are the powerful tag based filters, the capability to cope with very large collections, and the network protocol to control its operation. There is a full featured command-line client, a minimalistic GTK client, and a lirc client. Writing new clients should be easy with the supplied client libraries.
iCommune is an application that extends Apple's iTunes to share music over the network. It allows you to share the music in your iTunes library and access other iCommune music collections. iCommune music collections appear as playlists in your iTunes window. You can browse through them, and choose to stream or download the music they contain.