I use Reverse Single Crochet, or Crab Stitch, as an edging quite frequently in my patterns. I think it makes a pretty and sturdy edge to cardigans and sweaters. It looks fancy but it’s super easy! I always include writing instructions for it plus an illustration but some folks may find videos easier to follow.
This one is long but it is very clear! In this case, you do not ch 1 first because it is done in the round.
I really like the idea of using this edging on a coaster, kind of holds the glass in the center.
This video is shorter and uses the ch 1 to begin.