Gregorio is a project with a lot of functionalities. the main interest is gabc, a very simple and fast language to describe a gregorian chant score. the project is for now a command-line tool to convert gabc files into real score, like for example opustex or gregoriotex. but it also handles a xml format: gregorioxml. you can use the tool to read or write gabc and gregorioxml, and to write opustex and gregoriotex.