Briar
Briar is an E2EE messaging and publishing application designed for surveillance, censorship, and network-disruption threat models. It does not rely on a central message server.
Transport model
When the Internet is available, Briar synchronizes directly between contacts through Tor. During Internet outages, devices can synchronize over Bluetooth or Wi-Fi. Removable media can carry some shared material, and Briar Mailbox can support asynchronous delivery.
Contact lists and messages are stored on user devices. Forums and blogs replicate content among subscribers, which improves outage and takedown resistance but makes local device security and revocation important.
Best fit
Briar is the strongest fit in this comparison when blackout operation and resistance to traffic surveillance matter more than mainstream network effects. Its tradeoffs include contact bootstrapping, peer availability, device storage, and a narrower application ecosystem.
Secure and decentralized communication stacks places it beside server-based private messengers without treating them as the same topology.