Matrix is an open protocol for real-time communication. It is designed to allow users with accounts at one communications service provider to communicate with users of a different service provider via online chat, Voice over IP, and Videotelephony. Developed by Matrix.org
License: Open Source
Matrix.org is a decentralized communication protocol with a focus on security and flexibility, while Riot.im (now known as Element) is a user-friendly client built on top of the Matrix protocol that emphasizes ease of use and integration.