Look, does anyone remember Usenet?

You could run your own group. You could join any groups. It was up to your local Usenet admin which groups were carried at your site (usually a university or government domain) and how widely your local groups got promoted.

It was also up to you/your admin what you DIDN'T see in your usenet feed. Lots of sites didn't carry alt.sex.*, for example.

If your're old enough, "the fediverse" is kinda familiar.