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Open source / Slack

Open-source alternatives to Slack

Zulip, Mattermost and Rocket.Chat are open source: free to download and run on your own server. Slack costs from $7.25 a month, with a free plan.

Zulip

Open source (Apache-2.0) · Open-source team chat organised by topic

Zulip is team chat where every conversation has a topic, so live and asynchronous discussions stay easy to follow. You can run it on your own server or use the hosted version.

  • Topic-based threads inside channels
  • Works for live and asynchronous chat
  • Self-hosted or hosted cloud
  • Desktop and mobile apps
  • Large open-source community

Free to download and run on your own server under the Apache-2.0 licence; you pay only for your hosting.

See ZulipZulip vs SlackSource code (opens in a new tab)

Mattermost

Open core (MIT) · Self-hosted team chat with workflows, calls and AI

Mattermost is an open-core collaboration platform with chat, workflow automation, voice calls and screen sharing, built for organisations that need to run it on their own infrastructure.

  • Team chat and channels
  • Workflow automation (playbooks)
  • Voice calls and screen sharing
  • AI integration
  • Runs as a single Linux binary with PostgreSQL

The core is open source under the MIT licence and free to run on your own server; some enterprise features need a paid licence. A free cloud trial is also offered.

See MattermostMattermost vs SlackSource code (opens in a new tab)

Rocket.Chat

Open core (MIT) · Secure open-source chat for teams, partners and customers

Rocket.Chat is an open-source communications platform focused on data protection, used for internal team chat and for talking with other companies and customers.

  • Team chat and video calls
  • End-to-end encryption
  • Role and attribute-based access control
  • Self-hosted, cloud or air-gapped
  • Customer and partner channels

The core is open source under the MIT licence and free to run on your own server; some enterprise features need a paid licence.

See Rocket.ChatRocket.Chat vs SlackSource code (opens in a new tab)

Before you switch

  • Free to use, not free to run. The licence costs nothing, but self-hosting needs a server (often $5 to $40 a month) and someone to install updates and keep backups.
  • Open core means the main product is open source but some features, usually for larger teams, need a paid licence.
  • Hosted versions exist for many of these, run by the makers. They cost money but save the upkeep, and you can still move to your own server later.
  • Licences differ. MIT and Apache allow almost anything. GPL and AGPL require you to share changes you make to the code; for normal business use, that rarely matters.

More open-source alternatives