[an unfinished sandbox]
The various D&D settings or Worlds, have been depicted through various rules iterations, which are called Realities.
Boldface means that the World was featured in this Reality in a major way, such as with a campaign sourcebook or boxed set. Non-bold face means that the setting was only partly glimpsed, such in magazine or web articles, or brief "easter egg" style mentions)
The main D&D worlds:
Blackmoor: Original Reality [Blackmoor Supplement], First Fantasy Campaign Reality, Classic Reality (the DA modules), Third Edition Reality (and 3.5e reality shimmer), Fourth Edition Reality
Greyhawk: Original Reality, Classic Reality (B/X reality shimmer) [The B/X D&D adventures modules B1: In Search of the Unknown (featuring the Caverns of Quasqueton) and B2: The Keep on the Borderlands (with the Caves of Chaos) have suggested locations in Oerth], First Edition Reality, Second Edition Reality, Third Edition Reality, also the Transitive Reality (The official Reality wherein Oerth really morphed from the First Edition Reality to the Second Edition Reality in the Fate of Istus adventure).
Dark Sun: 2e Reality, 3e Reality, 4e Reality
Dragonlance: 1e Reality, SAGA Reality, 2e Reality (Chronicles adventures series), 3e Reality [+3.5 shimmer]. Also Transitive Reality (the Reality where Krynn's Reality really morphed from First Edition Reality into the SAGA System Reality and so forth. However, those 2e and 3e products which feature earlier times but don't use the "expected" 1e or SAGA rules, are depictions of the distinct Second Edition Reality and the Third Edition Reality.)
Mystara: Classic Reality, 2e Reality, 3e Reality (e.g. Dragon articles), 4e Reality (e.g. Bargle web-enhancement)
Forgotten Realms: 1e Reality, 2e Reality (and 2.5 S&P reality shimmer), 3e Reality, 4e Reality; Also Transitive Reality (the official FR reality, where the Toril's Reality really morphed through the Time of Troubles and the Spellplague; however, the Arcane Age products are the distinct 2e Reality).
Spelljammer: 2e Reality
Planescape 2e Reality, 3e Reality, 4e Reality
Birthright: 2e Reality
Eberron: 3e Reality (and 3.5 reality shimmer), 4e Reality
Nerath: 4e Reality, Elsir Vale (3e Reality)
Lesser-known worlds:
Pelinore: Classic Reality and 1e Reality [the Imagine magazine articles were dual-statted]
Ghostwalk: 3e Reality (and the 3.5 reality shimmer in the 3.5 Ghostwalk PDF update)
Jakandor: 2e Reality
Council of Worms: 2e Reality
Continuities/Multiverses:
The Classic Continuity and Multiverse. Up through 3e and possibly 4e.
The Dawn War Continuity and Multiverse. If the Dark Sun reboot is truly a reboot, then this is a distinct Multiverse.
The Second Sundering Continuity and Multiverse. The 5e continuity.
The Adventurers League Continuity and Multiverse. Reportedly somewhat different than the "canonical" timeline.
also various Alternate Continuities, such as the future Great War timeline of Mystara which was retconned.
licensed continuities:
The DMs Guild Continuities