http://mandelaeffect.com/
I stumbled across the Mandela Effect while looking for inspiration for my National Novel Writing Month novel. The Wiki entry for the Mandela Effect gets removed frequently, which causes no small amount of consternation among the believers. The basic gist of it is that we are shifting through dimensions, either physically or mentally, and there are subtle differences in reality that some people pick up on. One way that believers track the shifts is via celebrity deaths. The name 'Mandela Effect' comes from the belief that Nelson Mandela died in prison 20 years ago and that the current version of reality, which says that he was released from prison and became president of South Africa before dying a few years ago, is false. Other differences include the Berenstein/Berenstain Bears, Froot Loops/Fruit Loops, and McDonald's/MacDonald's.
Disclaimer: I am not a believer in this theory, so if I seem glib or dismissive, sorry.
Years ago, in my journeys across the fringe parts of the internet, among the Flat Earthers and Race War preppers, I found oblique references to time travel. These time travelers seemed to be doing so against their will, complaining of the headaches, nausea, and bloody noses that deja vu brought on. They tagged themselves via the names of celebrities that had died in their home realities, with names like Brimley98 and Cosby02. I figured it was just another kink. Seeing the Mandela Effect give name and form to this phenomenon elicits both a head shake and a slight smile from me.
On one hand, I can only think of one other branch of conspiracy theory that is easier to dismiss as mental illness, the DallasGoldbug school of all celebrities being the same actors. On the other hand, there's a certain cuteness to the idea that we are shifting time and space but the only markers are the names of TV shows (Sex in the City/Sex and the City) and when things happened (9/11 vs. 9/10). Clearly, the obvious answer is that these are people that cannot accept that their memories are perfect, so every single shred of evidence is clearly wrong. It does require a tremendous ego and large amount of solipsism to believe that a shift in reality is more possible than that you misrecalled the name of a children's book series.
Still, I find it interesting. What other ludicrousness is out there?