...://github.com/textbrowser/smokestack (Android)
https://github.com/textbrowser/spot-on (Desktop)
Smoke appears to be one of the first projects with an open source mobile encrypting chat server., an decentralized and easily-configurable chat server.
Smoke is known as the first mobile McEliece Messenger:
https://tarnkappe.info/artikel/english/mceliece-messaging-smoke-crypto-chat-the-first-mobile-mceliece-messenger-published-as-a-stable-prototype-worldwide-279847.html