Matrix is a protocol for enabling real-time communication between different service providers.
Pro End-to-end encryption
Matrix features end-to-end encrypted chats which are syncronized accross all your devices.
Pro Can be integrated with existing communication services
Matrix is designed to support Instant Messaging, VoIP/WebRTC signalling and Internet of Things communication and allows cross-communication between those services. Meaning one person could be using IRC and another Slack for IMs, or one person could be using Skype and another Google Hangouts for videoconferencing.