See http://recherche.ircam.fr/equipes/repmus/OpenMusic/ for more details.
OpenMusic was originally developped at IRCAM for MacOS using Macintosh Common Lisp (MCL). It was ported on Windows XP in 2005 (using Allegro Common Lisp).
The source code is distributed under the terms of the GPL.
A port to CMUCL on Linux was done by Gerardo M. Sarria M. and Jose Fernando Diago.
Another port to SBCL is to be released.
A port to Linux, using LispWorks, has been available since august 2013. See http://repmus.ircam.fr/openmusic/linux for more info.