[1] Sewing machines made before the mid-1950s mostly lack this hardware and so cannot natively produce a zigzag stitch.
The zigzagger's foot has longitudinal grooves on its underside, facing the material, which confer traction only sideways.
"YS Star" is a brand of Japanese sewing accessories that once included a zigzagger, model YS-7.
Its stitch pattern is controlled by small flat rectangular metal templates, seven of which are included.
Rather than using cams or templates, it is much simpler, offering just a single control for adjusting the bight (zigzag width).
It is composed the same way as a zigzag, except that the individual zig-zag pairs are each separated by several straight stitches.