I thought I'd mentioned this here before, but, if so, my search-fu wasn't sufficient to find it. It's a term coined by Diane Callahan for a sub-genre of fantastical fiction that (in my condensed version of her words):
1. Is set (except for the curio) in our world.
2. Has a "curio" -- a magical or scientific element -- that is generally unexplained and that serves primarily to generate the story; it's not explored in detail.
3. Focuses on human relationships-- often romance, but also other relationships, up to and including society.
Examples include:
-- time loop, e.g., Ground Hog Day,
-- body swap, e.g., Freaky Friday
-- near future technology, e.g., Flowers for Algernon
Also, reincarnation, time travel, telekinesis/clairvoyance, etc. Full list of her examples in her post here. Also, a great youtube she did here. In the video, she also walks through the process an author might go through in creating a curio story.
On SOL, I think a lot of do-over stories would fall in this category. I'm particularly thinking of Grey Wolf's Variations on a Theme series. Mind-control might also fit, although many of these seem to be more sex fantasies than explorations of relationships.
Do you, like Ms. Callahan (and me!) find this kind of story engaging? Are there other great examples of "curio fiction" here on SOL? (I'd love recommendations!)