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Last Updated: 07-17-2026 09:18 AM (UTC)

Mattermost

Teams that cannot send messages through someone else's cloud run Mattermost - the open-core, self-hosted alternative to Slack. It provides public and private channels, threaded discussions, unlimited search history, file sharing with previews, one-to-one audio calls, and screen sharing, with desktop clients for Windows, macOS, and Linux plus iOS and Android apps. Messages support full Markdown, which suits engineering conversations with code blocks and logs. Playbooks turn repeatable processes such as incident response and release management into checklist-driven workflows with automated triggers and retrospectives. Integration is a core strength: prebuilt connectors for GitHub, GitLab, Jira, ServiceNow, and PagerDuty, plus webhooks, slash commands, bots, a REST API, and a plugin marketplace with 700+ entries - together making it a working surface for ChatOps rather than just a chat room. Playbooks add keyword and event triggers, task assignment, status broadcasting, and post-incident retrospectives, so operational knowledge is not trapped in individuals' heads. The server is a single Go binary backed by PostgreSQL, with React clients, released monthly under MIT license and deployable fully air-gapped - which is why governments and defense organizations run it inside closed networks, and why the same control applies to any team with confidentiality requirements. The compiled Team Edition is free for unlimited users with no message history cutoff, so costs stay flat as the team grows.

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Benefits

  • No Per-Seat Fees or History Caps
  • The self-hosted Team Edition has no user limits and no message history cutoff, unlike Slack's free tier. Costs stay flat as the team grows.
  • Messages Stay Inside Your Perimeter
  • Every message, file, and call stays on your infrastructure. This is why governments and defense organizations run Mattermost in air-gapped networks; the same control applies to any team with confidentiality requirements.
  • Built for Engineering Conversations
  • Full Markdown in messages, syntax-highlighted code blocks, and native GitHub, GitLab, and Jira integrations make it a working surface for ChatOps rather than just a chat room.
  • Incidents Become Repeatable Processes
  • Playbooks codify incident response and release procedures into checklists with automated triggers and retrospective dashboards, so operational knowledge is not trapped in individuals' heads.

Features

  • Channels and Threaded Messaging
  • Public and private channels, group and direct messages, threaded discussions, unlimited search history, and custom emoji, available in 20+ languages.
  • Calls and Screen Sharing
  • One-to-one audio calls and screen sharing built into the platform, without routing conversations through an external conferencing service.
  • Playbooks for Workflow Automation
  • Checklist-driven runbooks with keyword and event triggers, task assignment, status broadcasting, and post-incident retrospectives.
  • 700+ Integrations
  • Prebuilt connectors for GitHub, GitLab, Jira, Zoom, ServiceNow, and PagerDuty, plus a plugin marketplace, webhooks, slash commands, and bot accounts.
  • Cross-Platform Clients
  • Web, Windows, macOS, and Linux desktop apps plus iOS and Android mobile apps with push notifications, all connecting to your instance.
  • Single-Binary Server on PostgreSQL
  • A Go server released monthly under MIT license, deployable via Docker, supporting high availability and fully offline air-gapped operation.