I recommend trying out Secure Scuttlebutt, which is a decentralized, FOSS p2p network. Click here for the White Paper. It does not actually require the internet to work, just any local network connection such as your home or a coffee house shared by users. Should also be possible to sync data via usb keys. For hosted public channels, or Pubs, you can host one yourself. It is asynchronous, similar to sending someone a letter they will open whenever they feel like it. Communication is able to thread together in a similar manner to Git commits. Main example is the original dev lives on a boat and only syncs to a public network every few weeks.
What happens is all data is synced fully encrypted and you will only be able to decrypt what you have access to via public/private keys. This could result in future congestion due to dramatic growth, but so far the network has remained small enough that it runs fine. Most popular client is Patchwork.
See this intro video as a love story: