Can I self-host an alternative to Slack?

Yes — Mattermost, Rocket.Chat, Element (Matrix) all support self-hosting. Most ship as Docker containers and run on any VPS.

Mattermost is open-source under MIT + Enterprise modules. You can self-host for free. Many also offer a hosted cloud option with a free tier and paid plans.

All alternatives

Team chat

Best Open-Source Alternatives to Slack

Q: What is the best open-source alternative to Slack?

The top open-source alternative to Slack is Mattermost: Mattermost is the closest Slack clone — channels, DMs, threads, integrations, mobile apps. Used by DoD, EU Parliament, regulated enterprises. Self-host in Docker, K8s-ready. Enterprise SSO/SAML/LDAP i

Slack is the team chat default. OSS alternatives matter for self-hosting (privacy/compliance), avoiding per-user pricing, and keeping data on-prem in regulated industries.

TL;DR — top pick

Mattermost

Mattermost is the closest Slack clone — channels, DMs, threads, integrations, mobile apps. Used by DoD, EU Parliament, regulated enterprises.

github.com/mattermost/mattermost

All 3 alternatives ranked

Mattermost

MIT + Enterprise modulesSelf-hostable★ ~30k

github.com/mattermost/mattermost

Mattermost is the closest Slack clone — channels, DMs, threads, integrations, mobile apps. Used by DoD, EU Parliament, regulated enterprises. Self-host in Docker, K8s-ready. Enterprise SSO/SAML/LDAP in the free version.

Pick Mattermost if

You need a Slack replacement for compliance/sovereignty reasons. Or you want to own your team's data.

Skip if

Your team is small and Slack free tier works fine — self-hosting has real overhead.

Rocket.Chat

MITSelf-hostable★ ~41k

github.com/RocketChat/Rocket.Chat

Rocket.Chat is similar to Mattermost but adds live chat / customer support widgets (so you can talk to customers AND internal team in one tool). Strong for hybrid use cases. More feature-rich but heavier.

Pick Rocket.Chat if

You need internal team chat + external customer support chat in one tool.

Skip if

You only need internal team chat — Mattermost is leaner.

Element (Matrix)

AGPL-3.0Self-hostable★ ~11k

github.com/element-hq/element-web

Element is the reference client for the Matrix protocol — federated, end-to-end encrypted by default, used by the French government and many security-sensitive orgs. Different paradigm (federated like email, not centralized like Slack).

Pick Element (Matrix) if

You need end-to-end encryption + federation across orgs (not just internal teams).

Skip if

You want Slack-clone simplicity — Mattermost is closer to that.

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