Inkscape uses an algorithm based on Dynadraw for it's calligraphic pencil tool. Which seems to extrude a scaled and rotated line along a path.
The algorithm others and I've been using uses an ellipse instead of a line. Which I prefer because it's closer to a real nib pen.
But my code doesn't output béziers yet, so I began playing with Tiller-Hanson's bézier offset algorithm.
But I'm not quite sure how to handle a rotated ellipse with a path offset algorithm.