As a small +1 — I built mood.site to be an easy way to share galleries of images with people. The idea being like "hey send me some photo inspiration for the party we're planning" and having a throwaway way to do that (kind of like a pastebin for images).
People definitely use it for this, but what has really surprised me is people's capactiy for expression inside of the bounds of the program I created, and how people are clearly using in as a sort of ad hoc social network of loosely collected boards and inspiration. There are no actual _social_ features in the app (no discovery, etc.), but what has been sort of inspriring is that The Will is just there for people to find ways of expression outside the idea of a "feed" and "posting".
I think those models have indeed become synonymous with "social media", but my only point here is to bring up a possibility of "social media" as something that can be much more expansive and look very different compared to the primary models we think of today.
Another person favorite of mine along the same lines is how the comments section of this Pilsburry recipe for "veggie pizza" has become it's own sort of ad-hoc social media for grandmas to share their own experiences with each other about the dish: https://www.pillsbury.com/recipes/veggie-pizza/4b2c60ae-69e5...