This page discusses a few of the existing major Minetest worlds.
Legends of Revival
Legends of Survival
Lord of the Test
Nexus of Worlds -- Includes HomeTown, Leyadel, Mauvebic World, New York City, Shadow Server (from ShadowNinja), and many others.
SONOS -- Includes both the major world that was lost with Steve Hosterman's death and the smaller Raspberry Pi world that preceded it.
Block City aka NRI World