I've heard of ETOPS, which permits the maximum duration for which a two-engined airplane can fly on one engine to the nearest airport.
Are 4-engined planes such as the Boeing 747 and Airbus A380 subject to any equivalent rules? If not, can these planes safely fly on just one engine for as long as needed?
Also, how are aircraft given different ETOPS certifications? What makes the 787 get ETOPS-330 and the 767 only ETOPS-180 despite the similarity in range and (to an extent) engine power and design?