Ask HN: What are decentralized Twitter alternatives?

Once upon a time Jack said that Twitter initially was very open in its early stages but eventually became much more centralized, and the scale of supporting such a centralized network in the future could be unsustainable. “Blockchain points to a series of decentralized solutions for open and durable hosting, governance, and even monetization,” he added. “Much work to be done, but the fundamentals are there.” Are there any truly decentralized social communication tools/protocols to look at?