There are many different timelines in the sonic fandom, and of course not all can be listed, but here are a few that are known. (Feel free to add if you wish)
The regular, canon timeline. This is where the official canon of fandom roleplays takes place.
Although it is the same world for the most part, in the Mobius-2 timeline many people and happenings in history are different. Example: In the main timeline, Drako the Zzinthine is a living weapon/alien. In Mobius-2, he is a normal mobian named Scorn Everburn who works at a government agency called Diamondbacks HQ as a field agent.
The timeline considered most similar to the normal Mobius timeline, Mobius-5 is where most non-canon roleplays take place.
One of the very different timelines, the only thing that is really worth noting is all the people in this timeline are the opposite gender of their regular timeline selves.
The timeline where its inhabitants are polar opposites to their usual selves. Example: A good character would be evil in this timeline, and vice versa.
Timeline where all mobians have gems somewhere on their bodies that grant them powers. Humans also do not exist.
The timeline where Nightmare devastates the planet. Cythan is an evil tyrant in this timeline. Visited in Temporal Shift.
Timeline where all mobians are just normal animals.Is sayed to be an past of Mobius.Purple Range the Cat came from this dimension.