The mpg123 distribution contains a real time MPEG 1.0/2.0/2.5 audio
player and decoder for layers 1,2 and 3 (most commonly MPEG 1.0
layer 3 aka MP3), as well as re-usable decoding and output libraries.
Among others, it works on GNU/Linux, MacOSX, the BSDs, Solaris, AIX,
HPUX, SGI Irix, OS/2 and Cygwin or plain MS Windows (not all more
exotic platforms tested regularily, but patches welcome).