This can be anything from Hyperspace in Star Wars, Warp Drive in Star Trek, travel through the Warp in Warhammer 40k or anything else.
I’ve always liked “slow” FTL travel, where going a few light-years still takes a few days or so. I also really like travel through an alternate dimension like in 40k, Event Horizon, Witchspace in Elite Dangerous.
I wanna know your favorite versions, or do you prefer stories that obey the laws of known physics, like the Expanse or Rimworld?
In the Bobibverse (book series) they used SUDAR for FTL. SUDAR was a gravity based communication. I believe this started coming out before the gravity wave discovery and we confirmed(/it became common knowledge) that gravity travels at the speed of light. It was a cool idea though.