Databag

Databag is a self-hosted messaging service. Notable features include:

Decentralized (direct communication between app and contact’s node)
Federated (accounts on different nodes can communicate)
Public-Private key based identity (not bound to any blockchain or hosting domain)
End-to-End encryption (the hosting admin cannot view sealed topics)
Audio and Video Calls (nat tranversal requires separate relay server)
Topic based threads (messages organized by topic not contacts)
Lightweight (server runs on a raspberry pi zero v1.3)
Low latency (use of websockets for push events to avoid polling)
Unlimited accounts per node (host for your whole family)
Mobile alerts (push notifications on new contacts, messages, and calls)