Signal is the world’s most widely used truly private messaging app, and our cryptographic technologies provide extra layers of privacy beyond the Signal app itself. Since launching in 2013, the Signal Protocol—our end-to-end encryption technology—has become the de facto standard for private commu...
There’s an IETF internet standard for federated messaging called XMPP. Just be compatible with the standard. It also allows for extensions if you offer more than the core spec.