Извините, почти на правах рекламы:
https://ring.cx/en• Open source
• Released under GPLv3 licence
• Supported by an active community
• A network
• OpenDHT protocol
• Decentralized communication
• Peer-to-peer discovery and connection
• Secured
• End-to-end encryption with authentification
• Identity managed by X.509 certificates
Based on RSA/AES/DTLS/SRTP technologies