It would be a tiny scrapbook app with the following features:
A little interface for creating little "posts" of pictures and text.
A list of friends to sync new post id's with.
A little interface to browse new posts of friends, add likes and comments.
Additional equally trivial features for creating shared scrapbooks for for events, clubs, topics, businesses, etc.
Each person's list of friend/group ids and posts would be held in the cloud with end-to-end encryption. The encryption would mean complete privacy for individuals, with only permissioned sharing to others.
Given the needs of a series of small posts, this is a trivial amount of data.
The app could be free with a small hosting fee of $1/month or something.
There would be no ads. No surveillance. No massive corporation doing groundbreaking work in AI in order to surveil and serve ads, promote engagement, manipulate users, then making a show of screwing up half hearted attempts to censor bad stuff that it had actively promoted due to its engagement properties.
The app's authors and cloud providers would simply have the incentive to make sharing scrap book posts fun for its users.
Let's call it "The Scrapbook". Wait ... drop the "the". It's just "Scrapbook". It's clean.