WebPlayer is a Web-based MP3 player, which runs as a server on any machine in your network, and can be controlled remotely via your web browser. Webplayer features the ability to load a playlist (.m3u) a directory of .mp3 files (non-recursively) or a single .mp3 file. Volume control (pcm and vol, tested only on FreeBSD) is also available. WebPlayer uses mpg123 as its mp3 player, via rmp3, but can also be modified to use mpg321 by changing line 151 of /usr/local/lib/ruby/site_ruby/1.6/rmp3/mp3play.rb to "mpg321 -v".
Borges requires Ruby (tested on 1.6.8), InstallPkg, WEBrick, Borges (or locally), and rmp3.