Previously Usenet. Which died under, ironically, trolls, antipornography drives, and copyright enforcement.

There was the WWW itself, at least for a time, though there are elements which tend toward centralisation, largely discovery, discussion, authentication, and directory.

Tim Berners-Lee and others have recently announce Solid.

https://solid.mit.edu

In my opinion, the whole idea of social networking is flawed. I don't need a network where people are interconnected ("webbed" together), I just need individual contacts and ephemeral groups. Ok, one can say that this implies that people are connected, and that multiple connections implies network, but the way this works on the Internet just doesn't feel right to me, especially with Facebook and so on. The elements of permanence and interconnectivity are just not done right. But as to how they should be done then, I haven't a clue.