What is "superworld"

Superworld is a superhero-themed role-playing game published by Chaosium in 1983. Written by Basic Role-Playing and RuneQuest author Steve Perrin, Superworld began as one third of the Worlds of Wonder product, which also included a generic fantasy setting, "Magic World", and a generic science fiction setting, "Future World", all using the same core Basic Role-Playing rules. Only Superworld became a game in its own right.