keychat on Nostr: 'Unlike traditional messaging apps, Briar doesn’t rely on a central server – ...

'Unlike traditional messaging apps, Briar doesn’t rely on a central server – messages are synchronized directly between the users’ devices. If the Internet’s down, Briar can sync via Bluetooth, Wi-Fi or memory cards, keeping the information flowing in a crisis. If the Internet’s up, Briar can sync via the Tor network, protecting users and their relationships from surveillance.'

Briar is great, but it requires both parties to be online at the same time to chat.