Zulip

Zulip is an open source team chat app for distributed teams of all sizes. Its topic-based threading combines email-style organization with chat, so conversations stay focused and easy to follow across both live and asynchronous work.

Messages are grouped into channels and then into topics within them, so people can catch up on exactly the threads they care about without losing context. Zulip self-hosts on Ubuntu or Debian Linux and in Docker, with prebuilt images for Digital Ocean and Render. A hosted Zulip Cloud option is available too.

Zulip is built by a distributed community of developers and licensed under Apache 2.0. Fortune 500 companies, large open source projects, and thousands of other organizations run it daily, on their own infrastructure or through Zulip Cloud.