Deejayd is a multi purpose media player that can be completely controlled through the network using XML messages. It suppports playlists, searching, and many media tags. It can playback many music and video formats using either its xine backend (recommended) or its GStreamer backend.
OpenDJMix is a virtual DJ system which allows you to mix MP3 files and audio CD tracks. It consists of a C++ API that manages a virtual sound bus with its I/O and a Qt GUI that enables a user to mix 4 MP3 or audio CD tracks. The API has been designed to be used in all multitrack sound tools.
1FCD-OpBSD (also known as Karma BSD) is a one-floppy OpenBSD MP3 player with functionality to mount NTFS, UDF (on DVD, CDROM, or external file), EXT2FS, NFS, MFS, and MSDOS file systems. It plays MP3 tracks, and can copy files from any disk to any disk. The software may be useful for the blind and it can also be used as a unique utility for copying files over a network (via NFS) or from any file system known to OpenBSD. USB sticks can be mounted as well. Static OpenBSD binaries can be made on other systems and used with Karma BSD.
SvOlli's Little Audio Related Thingies, or SLART for short, is a compilation of rather simple programs that are related to audio files: it consists of a player (Partyman), a CD ripper, a tag editor, and some other tools. These programs can communicate with each other via a custom IPC bus, so a newly ripped track can be automatically queued in the player, for example.
Coherence is a set of DLNA/UPnP devices, like MediaServer and MediaRenderer. In addition, it includes a well-designed framework to extend other applications with DLNA/UPnP functionality. It also has an emerging DBus API, enabling these applications to participate in digital living networks. It supports Playstation 3 (PS3), XBox, and many other devices.