What and why Koblitz curves?

Answer to this post #1 (from “Software Implementation of Elliptic Curve Cryptography over Binary Fields” – Darrel Hankerson, Julio Lopez Hernandez and Alfred Menezes):

Koblitz curves are elliptic curves defined over F_2 . The primary advantage of Koblitz curve is that point multiplication algorithms can be devised that do not use any point doublings.