IRC is an interesting example to use here. IRC isn't and never was federated. It is a centralized chat protocol where you connect to isolated networks. Simila

IRC is an interesting example to use here. IRC isn't and never was federated. It is a centralized chat protocol where you connect to isolated networks. Similarly Matrix is making massively huge gains in the chat space and is federated. It's not taking over slack or discord yet, but is gaining features and ground.