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
Zulip is focused on real-time messaging with a unique threaded conversation model that benefits team collaboration, while Matrix.org emphasizes decentralization and security with end-to-end encryption. Both platforms cater to different use cases with their unique strengths.