Mattermost is the leading self-hostable team chat platform for security-conscious engineering, DevSecOps and defense teams. The Team Edition is free and MIT-licensed; commercial Professional starts at $10 per user per month.
Mattermost is an open-source, self-hostable team collaboration platform that has positioned itself as the Slack alternative for security-conscious engineering, DevSecOps and defense teams in 2026. We rate it 82/100 — the right pick if you need to keep chat data on your own infrastructure, integrate deeply with Git and incident-response tooling, and never see a Slack invoice scale linearly with seats.
Mattermost was founded in 2016 by Ian Tien and the SpinPunch team after their internal chat tool was open-sourced and overshadowed the gaming startup it served. The project lives on GitHub at github.com/mattermost/mattermost with 36,490+ stars, 8,580+ forks and 849 open issues. The Team Edition ships under an MIT license as a single Linux binary with PostgreSQL; the Enterprise Edition is a commercial superset distributed under a source-available license.
The pitch in 2026 is sharper than "self-hosted Slack." Mattermost has been aggressively repositioned as a collaboration platform for "mission critical work" — the U.S. Department of Defense, intelligence agencies, banks, and air-gapped industrial-control teams who need on-prem deployment, FIPS-140-2 cryptography, SCIF-friendly mobile clients, and the ability to keep working when the public internet does not. The latest stable release is v11.6.1, published on , and v10.11 remains the long-term Extended Support Release through August 15, 2026.
Sentiment in 2026 is broadly positive but specific. On Reddit's r/selfhosted, the most upvoted Mattermost threads praise the "one binary, one Postgres" deployment story and the fact that the free Team Edition is the real product, not a hobble-ware tier. On G2, Mattermost averages 4.2/5 across 400+ reviews with reviewers consistently citing data sovereignty and GitLab/Jira integrations as the two reasons they switched from Slack. On Hacker News, a recurring developer take is that Mattermost is "not as polished as Slack but never bills you per ex-employee" — exactly what infrastructure teams want.
The recurring complaints are also consistent. Push notifications on the self-hosted edition are a known sore spot — the proxied APNs/FCM relay through Mattermost's hosted notification service is not always reliable, and rolling your own is painful. Search is functional but markedly weaker than Slack's; the experimental Bleve search backend was retired in v10. The mobile app has stabilised after a rocky 2022, but long-running iOS sessions can still drop background connections in restrictive networks.
Mattermost charges per active user per month on its commercial plans. The Team Edition is free forever, MIT-licensed, and capped at 250 users in the recommended deployment guide. Enterprise pricing is contact-sales but reliably anchored around the published $20 list price.
| Plan | Price | Key Limits |
|---|---|---|
| Team Edition (self-hosted) | $0 forever | Unlimited messages, MIT-licensed, recommended for <250 users, no SSO/audit/compliance |
| Professional | $10 per user/month | SSO, guest accounts, advanced permissions, read receipts, 24/5 support |
| Enterprise | $20 per user/month (contact sales) | FIPS, SAML, AD/LDAP, compliance exports, customer-managed keys, 24/7 support |
| Enterprise Advanced | Custom (contact sales) | Air-gapped, classified-network deployment, dedicated TAM, premium support |
Best for: security-conscious engineering and DevSecOps teams, regulated industries (defense, finance, healthcare), and any organisation where chat data leaving the corporate network is a non-starter. Particularly strong for teams already running GitLab, Jira and PagerDuty who want ChatOps without paying Slack Enterprise prices.
Not ideal for: small marketing or sales teams that want polished onboarding, rich third-party app ecosystems, and someone else to run the infrastructure — Slack remains the smoother landing for non-technical users. Self-hosting Mattermost is genuinely an operations job, not a one-click affair.
Pros:
Cons:
The obvious alternatives are Slack for non-technical teams that want the most polished SaaS experience and accept per-seat pricing, Rocket.Chat for self-hosters who want a broader feature surface (built-in video, livechat, omnichannel) at the cost of higher resource usage, and Zulip for engineering teams that prefer threaded-by-default conversations and topic-based organisation.
Yes — if your threat model includes "chat vendor compromise" or your compliance team has a copy of NIST 800-53 on the wall. Mattermost is the only open chat platform with credible defense-grade deployment options, and the Team Edition is genuinely free forever. If you are a 12-person startup with no DevOps owner and a marketing team that lives in Slack DMs, pay for Slack and move on. The 82/100 reflects an excellent product with rough edges in mobile push, search and onboarding — fixable problems Mattermost has been steadily chipping away at across the v10 and v11 release trains.
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