MaGnuX MP3 Control Server is a server that allows you to control the playing of MP3 songs. It uses mpg123 to play the songs, and features playlist management, a builtin Web server, IP-based access control, and much more. It's written entirely in Ruby, which makes it extremely flexible and very easy to extended.
Aurion Music Manager (AMM) has been designed to be a very user-friendly interface for using mpg123, cdrecord, mkisofs, lame, and other very powerful command-line music tools. It uses the SDL for its graphics, and the interface can use the TV output capability featured by several video cards. AMM also includes a WAV file player, called pwav123.
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.
QSMP3 is a MP3 Playback component for Delphi and Kylix. It allows you to add full MP3 playback capabilities to your application under both Win32 and Linux. It is a non-visual component, so it should be functional under Linux CLI, X11, Win32 GUI, and Win32 (not DOS) CLI. Supported capabilities include playback, stop, pause, seek-by-time-index,seek-by-byte-indes, automatic position reporting (by event), and position reporting by function call. This component relies on SDL, SMPEG, and the JEDI-SDL translation of the SDL and SMPEG headers to Pascal.
zlplay is an MP3 player that uses the zlcatalog system to organize songs. zlcatalog is a library for organizing things in non-hierarchical ways. Songs in zlplay can belong to multiple groups. Navigation through the groups shows songs and related groups. So, for example, it's very easy to start listening to all of your songs randomly and then when you hear a song by a particular artist, a single click switches the song list to songs by that artist.
NP3 Music Player is a standalone music player, which has a distinct separation between client and server. It consists of a daemon, which plays the files (through XMMS input plugins), and is controlled by a client. It features an event system, which enables excellent support for sophisticated clients.