This is for any anime/manga that has created another series within itself that is referenced quite often.
Gunvarrel is a popular mech in Robotics;Notes franchise. Its last episode has never been aired.
Meruru (メルル, Meruru) is Kirino's favorite magical girl from the anime series called Stardust☆Witch Meruru.
Nyapollen is an animated show that Misaki created, and the gang used it during the cultural festival.