This turns the font into a whole bunch of polylines where the curves are defined by splines, but they are very short segements, but the letters are not all one complete polyline, they are comprised of 2 to 4 segments, depending upon the letter.
If it displays as a 'normal' O it is not a real single line font ,as a true single line letter O will render as a filled circle on a normal graphics package as there would only be a single outer boundary.
that cricut does a great job drawing think subway art, or posters• Each producer would make its own small compiler, which every archival font would compile in its fonts-format.