Best open-source alternatives to Discord

Zulip is an open-source team chat platform designed to help organizations manage both real-time and asynchronous communication in a more structured way than traditional chat apps. Its signature feature is topic-based threading, which keeps conversations organized and makes it easier for distributed teams to follow multiple discussions without losing context. The project is aimed at teams, open-source communities, and other organizations that need productive group communication. The README highlights self-hosting on Ubuntu or Debian Linux, deployment via Docker, and hosted cloud options through Zulip Cloud. It also emphasizes a large contributor community and extensive documentation for both code and non-code contributions, suggesting a mature project with a broad user and developer ecosystem.