You might be interested in Keychat. Keychat is a chat app, built on Bitcoin Ecash, Nostr Protocol and Signal Protocol. Keychat is inspired by the postal system — stamps, post offices, letters. Keychat uses Bitcoin ecash as stamps and Nostr relays as post offices. Keychat uses Signal protocol to ensure message encryption security and meta-data privacy. https://www.keychat.io/