The AU Dictionary

All AU's Begining with S

Single Parent AU: In which a character has a child or becomes a parent in someway and raises them on their own.

Soulmates AU: There is seriously lots of different Soulmate prompts. Is when two (or more) characters are fated to be together, sometimes through multiple lives and/or into the afterlife. Sometimes but not always, the pairing might have a characteristic that helps them to find each other, such as identical or complementary birthmarks, tattoos, scars, half necklaces that the other person has the other side. Some stories only need a character to hear (or just see) their soulmate to know who they are.

Space AU: Where a fandom that is canonically set on Earth becomes set in outer space.

Spider-Man/Deadpool AU: When one character is Spider-Man and their lover/rival are either a regular human or is Deadpool.

Spy AU: Also known as Secret Agent AU or Espionage AU. The whole cast is turned into spies, sometimes they work for the same organization, government or they operate independently. Other times the AU is focused on only one or two characters that are the spies.

Superpowers AU: In which the characters have superpowers and are either heroes and/or villains.

Steampunk AU: In which a story is turned into a futuristic/sci-fi version of a 19th Century, usually Victorian or Edwardian containing clocks, gears, springs, steam power, analog computers, airships, etc.