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Mattermost

★ 32k

The self-hosted Slack for teams that need compliance: playbooks, boards, and a single Go binary at its core.

Mattermost does the job of Slack, self-hosted. It is AGPL-licensed, so a hosted fork has to publish its changes, and setting it up is an afternoon, not a weekend. Slack bills $10/user/mo for it. 32k stars on GitHub.

Open-source replacement for Slack.

Licence
MIT / AGPL
Self-hosting
Medium
The paid one costs
$10/user/mo
GitHub stars
32k
view the code →official site →

Is it actually a replacement?

We have written a verdict on what it replaces — what you lose, and why people still pay:

How Mattermost runs

Where it runs

Mattermost runs on your server.

Installing it

Install the official Linux binary with PostgreSQL, then configure systemd, TLS/reverse proxy, SMTP, and file storage.

Where your data lives

Channels, posts, users, and configuration live in PostgreSQL; file attachments live in the Mattermost data directory or configured S3-compatible object storage.

What setup takes

The first obstacle is a real Linux service deployment, PostgreSQL, SMTP, DNS/TLS, storage, backups, and upgrades, not an app-store install.

The catch compared with Mattermost Professional

Team Edition keeps the core chat product, but Professional features such as enterprise authentication, advanced compliance and administration, support, and larger-scale assurances are absent.

Mattermost questions

Is Mattermost open source?

Yes — it is released under MIT / AGPL.

Can Mattermost replace Slack?

Our verdict on Slack Pro is YES. Rocket.Chat Community (46k stars), Discourse (44k stars), Mattermost Team Edition (39k stars) are mature open-source replacements for Slack Pro — self-host with real ops work and stop paying $8.75/mo.

Can I self-host Mattermost?

Yes — we rate it medium to self-host, and it runs on your server. Install the official Linux binary with PostgreSQL, then configure systemd, TLS/reverse proxy, SMTP, and file storage.

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