I spent all of high school on hotline servers but it was never very decentralized. Not compared to a real federated protocol. It's client-server where servers register themselves with trackers which keep lists of server and return the list to clients when they ask.

KDX is the "modern" open source implementation of the Hotline/Caracho concept.

I still think usenet is the way to go. It's a robust federated system. Sure most people will use a few servers but there's always the easy open to switch to a new one. I even posted on misc.invest.stocks today using eternal-september.org text only access.