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/