Threats are everywhere, including from alternate universes. Agent Olivia Dunham becomes part of the FBI's Fringe Division and is tasked with saving us from these threats.
Family Guy - "Road to the Multiverse"
Not surprisingly, Stewie has a remote control that takes him and Brian on a trippy ride to various alternate universes, including one where the Griffin's live in a Disney version. Eventually they end up in a universe where dogs rule. Brian doesn't want to leave and breaks the remote seemingly forcing them to stay, at least for a bit before heading back to reality.
After a car accident, a detective lives in two realities: one where his wife survived and the other where his son survived. He solves crimes in both realities in order to keep them both of them alive. The series aired for one season on NBC.
The O.C. - "Christmukk-huh?"
Ryan and Taylor get injured while putting up Christmas decorations and in their dream state we enter an alternate reality where Ryan doesn't exist.
Friends - "The One That Could Have Been"
A two-part "what if" episode that sends us to an alternate reality when Rachel learns that her ex is getting divorced and she wonders outloud what life would have been like had she married the guy. This causes all the other friends to have what-if moments of their own, including one where Monica imagines a world where she is overweight.
The Man in the High Castle
What would life in the U.S. be like if the Nazi's won World War II? This question is pondered on this netflix original series based on Phlip K. Dick's Hugo Award-winning novel of the same name. Set in 1962, 17 years after the War ended, it shows us an America divided with Japan controlling the west, Germany controlling the east, and a "neutral" zone right down the middle. Scary stuff, indeed.