Gregorio, is a free software used to design Gregorian scores. It is structured like LaTeX or Lylipond, with a source which is compiled to produce .pdf files. See more details on http://home.gna.org/gregorio/ Gregorio is some kind of cousin of LilyPond but is specialized for gregorian scores.
A plug-in has been written to allow to use Gregorio under Scribus similar to the LilyPond one. The combination of Gregorio and Scribus gives a fine flexibility for people wanting to include Gregorian scores in Scribus documents. See more details in http://home.gna.org/gregorio/scribus
