Welcome to the Alternity Master List.
Here you will find my list of alternate realities, imaginary stories, possible futures and crossovers.
The criteria for the list are very simple. The world has to be connected in some way to the core Earth of either Marvel or DC and be an alternate version of that world.
Rex Mundi and Arrowsmith, for example, are both very good alternate world stories, but have no connection to the main DCU or MU, and are not included.
This list is going to always be a work in progress, so if you have a suggestion or want to help with a description, be sure to e-mail me.
Note that I have adopted the naming convention of the Appendix to the Marvel Universe. i.e.: Earth-Morgan Conquest, Earth-Bishop Last X-man, etc...
I do not use the numbering convention of Blaklion's Chronology Compendium unless those Earths are named that way in a comic book. i.e. DC Pre-Crisis Earth-1, Earth-2, Earth-3, etc...
Cartoons, movies, TV shows and their alternates are listed ONLY if there is a comic book adaptation. The X-men movies and Teen Titans cartoon are included, the old Adam West Batman show, sadly, is not.

6 degrees of separation

So how do some of these non-DC/Marvel worlds connect to the two big guys?

Straight Alternate. If a character exists in universe A and a recognizable version of the character exists in universe B, then those universes are alternates of each other. Some characters, such as Dracula, Frankenstein, Doc Savage, the Shadow and the Lone Ranger fit this idea, and thus all their appearances can link their universes back to the main pair.

Crossovers. If a character from universe A has crossed over to DC or Marvel and a character from universe B has crossed over to universe A, then that character has a connection to DC/Marvel. In theory, that character could travel all the way across universes to DC/Marvel. This holds true no matter how far away from the DC and Marvel Universes you get. As long as there's a connection. Sometimes, instead of a character actually traveling to a new universe, characters from separate universes exists side by side in a merged universe. Since this is a straight alternate, it counts.

Multiple publication. If the same universe is published by the same or different companies with enough differences that it might be considered a separate universe, then it's included. It's the same principle as including what ifs and elseworlds. It's the same Earth and the same characters, things just turned out slightly different.

Fictional reference. This is the most tenuous connection. If universe A contains a comic, movie, novel, etc. of the characters of universe B, then there might be a connection. This principle originated at DC when the Flash of Earth-1(Barry Allen) met the Flash of Earth-2(Jay Garrick), who Barry remembered reading about in comics. The explanation was that the writers and artists of Earth-1 were 'attuned' to Earth-2. This idea has been used on several occasions and I see no reason not to extend it to other universes, especially if different universes are published by the same company. This isn't a hard and fast rule, and I'll be using my best judgment.