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Open-source alternative to Slack

Mattermost is a free, open-source Slack alternative with channels, threads, calls and your full message history. Slack’s free plan hides messages older than 90 days and paid plans charge per user; self-hosted Mattermost does neither.

1 alternative Free app Our pick: Mattermost

At a glance

App Good for Code Import from Slack Ease of use
Mattermost Small teams that want Slack-style chat with unlimited history on their own server Code Open source Import from Slack Partly Easy

Why look for an alternative to Slack?

Slack is the best-known team chat app: channels for topics and projects, threads, direct messages, huddles for calls and a large directory of integrations.

Teams look for an alternative mostly because of price and history. The free plan only shows the last 90 days of messages and files, so older decisions and documents disappear from view unless you pay. Paid plans are charged per active user each month, which adds up as a team grows. Some organisations also need their conversations kept on their own servers for privacy or compliance. A self-hosted chat app such as Mattermost keeps your full history, has no price per user in its free edition, and stores every message on your own server.

How Mattermost compares

Mattermost

Open-source team chat like Slack, with your full history kept.

The closest self-hosted match to Slack. Channels, threads, direct messages, reactions, file sharing, search and desktop and phone apps all work the way Slack users expect, and your whole message history stays searchable.

What you gain
  • Your full message history is kept, with no paid plan to unlock it
  • No price per user
  • Messages and files stay on your own server
What is different
  • Fewer ready-made integrations than Slack
  • The free edition is meant for teams under 250 active users
  • Voice calls are limited to one-to-one in the free edition and need extra network setup
Easy Open source · MIT
Deploy Mattermost About Mattermost

Moving from Slack

Mattermost can import a Slack workspace export, with public channels, messages, threads and files. The conversion uses Mattermost's free mmetl tool and the mmctl command line, so it takes some technical work; many small teams simply start fresh and keep Slack read-only for a while. Recreate your channels, invite the team, and connect the integrations you rely on through webhooks or Mattermost's plugin marketplace.

Questions

What is the best open-source alternative to Slack?

Mattermost is the free, open-source alternative to Slack for team chat in the catalogue today. The closest self-hosted match to Slack. Channels, threads, direct messages, reactions, file sharing, search and desktop and phone apps all work the way Slack users expect, and your whole message history stays searchable.

Does Mattermost have desktop and phone apps?

Yes. Mattermost has free apps for Windows, macOS, Linux, iOS and Android, and works in any web browser.

Can Mattermost do calls like Slack huddles?

The free edition includes one-to-one voice calls, which need some network setup. Group calls are in Mattermost's paid editions.

Is it really free?

Yes, the app is free. To run them you need Cloudgate and a server. Use hosted Cloudgate, which can also provide the server, or install Cloudgate on a server of your own for free. Cloudgate's plans and prices are at cloudgate.octabyte.io/pricing. One server can run several apps.

Do I need a developer?

No. Cloudgate installs the app on your server and gives it a secure web address. You use it in your browser.