Fudge is a role-playing game engine/framework with which many settings and games can be made. For more information on Fudge, please see: https://www.fudgerpg.comFor the base Fudge rules and system guide (with lots of useful extra info for making your own settings), I heavily recoomend the Fudge 10th Anniversary book.
I have created several games and associated settings using Fudge.
A Magical world with monsters and creatures where the players are adventurers travelling the world and pursuing quests.
A high-tech Sci-fi setting where the players each command and control their own starship.
A high tech Sci-fi setting where the player characters are the senior staff and crew aboard a starship.