Multiverse/Pre-SGW

The Multiverse is the collective name of all of the alternate zones and different realities that exist in conjunction with the world of Sonic the Hedgehog. These include different versions of the same dimension or vastly different ones, often accessible only through advanced science or powerful magic.

Description
The Prime Zone is the center of the multiverse, with all other zones surrounding it being derived from their Prime counterpart.The amount of alternate zones in the multiverse was unknown, possibly infinite, but all were previously monitored and protected by the Zone Cops Corps of the No Zone. (StH: #11, SSS: #8,#10)

When Doctor Eggman launched the Super Genesis Wave, it caused the entire multiverse to collapse in upon itself and reboot, and almost all of the zones that existed before were destroyed. Known exceptions include the Prime Zone, which suffered serious changes in it's history, and the Sol Zone. The inhabitants of the Prime Zone would later encounter another reality with inhabitants similar to themselves. (StH #256; SU: #55; SB: #9)

There are other multiverses that exist independently from the one containing Sonic's world, such as the dimension of Earth 20XX and possibly an unnamed world inhabited by various superheroes. Normally these multiverses are incapable of contact with each other, and it has only been the efforts of villains such as Dr. Eggman or Dr. Albert W. Wily that have made it possible. (MM: #24, SU: #51, StH: #248, SSS: #7)

Background Information

 * Ian Flynn revealed in a Q&A that most of the zones that existed prior to Worlds Collide have been destroyed. He has also indicated that the Sol Zone's Jeweled Scepter is the reason that zone has merely been altered, rather than wiped from existence. The Q&A also revealed that Worlds Unite may end up showing a whole new multiverse.
 * However, aside from the Sonic Boom Zone, it seemed that no other zones in Sonic's multiverse appeared during the crossover. Although it did introduce the concept of a Nexus.
 * In a previous Q&A, Ian Flynn indicated that if the Prime Zone were to be destroyed, no other alternate zones would come into existence. This was in response to a query inspired by the release of the recent Teenage Mutant Ninja Turtles animated film, Turtles Forever, in which the original Mirage Comics universe was deemed "Turtle Prime" and that, if it was destroyed, all others would follow.