Octagram

The octagram, or og, is a non-convex polygon with 8 sides. It's created by stellating the octagon. A regular octagram has equal sides and equal angles.

Vertex coordinates
Coordinates for an octagon of unit edge length, centered at the origin, are all sign changes and permutations of
 * (±($\sqrt{2–√2}$–1)/2, ±1/2).