I have not seen this posted here, so let me. I found a pretty good piece of free software for download which puts a lot of things together. It will not only compose in Gregorian square notation but also add St Gallen notion above or below the square, and insert text in different type fonts, and has some pretty fancy first letter incipits. Even 14th century notation is possible. It is in French, but is pretty straightforward and intuitive:
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