Mattermost

What it is

Mattermost is a Slack-style chat platform with teams, channels, threads, custom emoji, group calls and screen sharing, playbooks, and integrations with Jira, GitHub and GitLab, built to run on your own infrastructure, including private cloud and air-gapped networks. Free options: Team Edition (the MIT-compiled open-source build, up to 250 users, no SSO and no paid support) and Entry, the default free edition since October 2025, which includes enterprise features but shows and searches only the latest 10,000 messages across channels, limits calls to 40 minutes and is meant for teams under about 50. Paid plans are Professional (SSO with SAML or OIDC, AD/LDAP sync, guest accounts, next-business-day support), Enterprise (compliance export, legal hold, data retention, high availability) and Enterprise Advanced; mattermost.com no longer lists prices and routes buyers to sales (Professional was publicly listed at $10 per user a month billed yearly). Mattermost Cloud is offered only as a single-tenant Enterprise service. It imports Slack export files with its mmctl tool. Web, Windows, macOS, Linux, iOS and Android. Checked November 12, 2026 on mattermost.com and its documentation.

Best for

• Engineering, security and operations teams
• Organizations that must keep chat on their own servers
• Air-gapped, government and regulated environments

What we like

• Self-hosted: messages stay on your infrastructure
• Familiar Slack-like channels, threads and shortcuts
• Imports Slack exports
• Strong DevOps integrations and playbooks

What to watch

• You install, update, back up and scale the server yourself
• Free Entry edition caps visible history at 10,000 messages; Team Edition lacks SSO
• Prices are quote-only now, and paid plans are annual
• Fewer ready-made integrations than Slack, and a plainer interface