Sorry, I guess I should have been clearer, I was talking about stuff that was specifically written as an alternate universe version of the characters, so things like Marvel Noir, Red Son, Bombshells, Marvel 1602 and DC's Earth One GNs and All-Star series.
So the DCEU Superman wouldn't count since he's that universe's main version.
Well, to be a bit pedantic, every character is the generally the main version of the character in their universe. You're not allowed to use the red Son Superman under your rules, because he is the main superman of his universe. Also, I think that unfairly disqualifies radically different versions of heroes, like the New 52 versions of some characters I'd mentioned. Maybe you should have said "Superheroes from universes outside of and of the mainstream universes" or something like that, and to that much more restrictive question my Batman, Wonder Woman and Hulk picks still count, but I'll stand by my other ones as well.