Zulip

Zulip is an open source team chat application built around topic-based threading, positioned as an alternative to Slack for teams that want organized, searchable conversation history. Every message belongs to a topic inside a channel (called a stream), which keeps parallel conversations readable instead of collapsing everything into a single scrolling feed. Zulip is built and maintained by a large, distributed open source community and describes itself as the largest and fastest-growing open source team chat project.

Key features

• Topic-based threading: messages are grouped into topics within streams, so multiple conversations can happen in the same channel without interleaving.
• Built for live and async use: designed to work as well for real-time chat as it does for catching up on missed conversation later, which the project calls its unique approach to organizing conversations.
• Large, active contributor base: more than 1,500 contributors merge over 500 commits a month, with 99+ people having each contributed 100+ commits, and 100% Mypy type coverage on the Python codebase.
• Self-hosting options: install directly on Ubuntu or Debian Linux, run via the official Docker image, or deploy prebuilt images to Digital Ocean or Render.
• Zulip Cloud hosting: managed hosting is available, with free Zulip Cloud Standard offered to hundreds of qualifying organizations, including other open source projects.
• Extensive documentation: over 185,000 words of contributor documentation covering the codebase and development workflow.
• Non-code contribution paths: reporting issues, translating the app, and giving product feedback are documented alongside code contribution.

Ideal use cases

Zulip is used by Fortune 500 companies and open source projects such as Rust, and it targets organizations that need structured conversation across time zones rather than a single always-on chat room. Remote and distributed teams that rely on catching up asynchronously benefit from the topic model, since a topic can be read start-to-finish without scrolling through unrelated messages. Organizations evaluating Zulip can try it without an account in the public development community chat.

Self-hosting and deployment

Beyond a direct Ubuntu/Debian install, Zulip supports Docker via the zulip/docker-zulip project and one-click marketplace listings for Digital Ocean and Render. Development builds are tracked with GitHub Actions CI, Codecov coverage reporting, and Ruff and Prettier for code style enforcement. Teams that don't want to run their own server can use Zulip Cloud instead, choosing between the paid Zulip Cloud Standard plan and other Zulip Cloud hosting tiers documented on the pricing page.

Outreach programs such as Google Summer of Code give newcomers a structured path into the codebase, and the project publishes its progress on a public blog alongside a presence on LinkedIn, Mastodon, and X. Users can also support the project financially or by helping others discover it, both listed as ways to support Zulip long-term.

Zulip is distributed under the Apache 2.0 license.