Twitter is a popular social networking service where users can write short messages in a one-to-many fashion (you can read more about it at Wikipedia). I've been reading an interesting article by Alex Payne (former API Lead at Twitter), The Very Last Thing I’ll Write About Twitter, where he argues for a decentralized one-to-many communications mechanism...
From a programming perspective, how would this service be designed? I imagine it could be similar to email, where anyone can set up a mail server. However, one of the major motivations is to resist censorship; can the architecture be fully decentralized? It would involve a similar protocol to the open standards-based protocols behind email and IM; does such a protocol already exist? Should the design include aspects of an anonymity network such as Tor? Has an open-source initiative already begun for this?
I'm making this a community wiki, as these are rather open-ended questions about the design of a decentralized one-to-many communication service.