A powerful package which allows the typesetting of polyphonic and other multiple-stave music is MusicTeX, written by Daniel Taupin (taupin@rsovax.lps.u-psud.fr). It is available in macros/musictex
In the recent past, Daniel (as well as with various other people, notably Ross Mitchell and Andreas Egler) have been working on a development of MusicTeX, known as MusiXTeX. MusiXTeX is a three-pass system (with a processor program that computes values for the element spacing in the music), and achieves finer control than is possible in the unmodified TeX-based mechanism that MusicTeX uses. Daniel Taupin and Andreas Egler are pursuing distinct versions of MusiXTeX; they are available, respectively, from macros/musixtex/taupin and macros/musixtex/egler
Digital music fans can typeset notation for their efforts by using midi2tex, which translates MIDI data files into MusicTeX source code. It is available from support/midi2tex
A rather simpler notation than MusicTeX is supported by abc2mtex;
this is a package designed to notate tunes stored in an ASCII format
(abc notation). It was designed primarily for folk and traditional
tunes of Western European origin (such as Irish, English and Scottish)
which can be written on one stave in standard classical notation.
However, it should be extendable to many other types of music. It is
available from support/abc2mtex
There is a mailing list for discussion of typesetting music in TeX.
To subscribe, send mail to mutex-request@stolaf.edu containing
the word `subscribe' in the body.