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Mattermost
AGPL-3.0Mattermost is an open-source alternative to Slack and Teams that delivers secure team messaging, boards, and incident workflows with self-hosted control.
Open-source alternative to — compare it against:
Overview
Mattermost runs on a Go backend paired with a PostgreSQL database, serving organized team messaging from a single compiled binary on internal infrastructure. Originally developed in 2015 to replace an internal chat tool at gaming studio SpinPunch, the project has grown to more than 39,000 GitHub stars. For operations leads and privacy-conscious teams, this architecture provides direct custody of message logs, attachments, and credentials behind private firewalls.
Why Mattermost instead of Slack
Slack operates as a multi-tenant cloud service, retaining message archives, uploaded files, and search telemetry on remote infrastructure. For engineering teams and agencies subject to regulatory compliance or non-disclosure agreements, cloud tenancy creates audit exposure and data residency friction. Mattermost provides a familiar channel layout, threads, direct messages, and webhooks, but installs on internal Linux servers, private Kubernetes clusters, or virtual machines. Network traffic remains local, and encryption keys never leave internal systems.
Slack enforces steep monthly seat fees on paid tiers while restricting search history on free plans to ninety days, penalizing agencies working with external contractors. Mattermost removes artificial message history caps and seat fees on self-hosted servers, enabling permanent, searchable chat archives on private storage. Slack retains an edge in commercial app integrations and turnkey mobile push. Mattermost requires admins to run a push proxy or relay alerts through Mattermost servers to reach mobile devices, trading hands-on maintenance for complete data control.
What it does well
- Complete data residency: Operations leads keep chat archives, attachments, and user records inside a PostgreSQL database behind corporate firewalls.
- Slack-compatible webhooks: Engineering teams migrate custom alert scripts, deployment bots, and monitoring hooks with minimal changes to payload URLs.
- Integrated boards and playbooks: Teams manage incident response checklists and track project tasks directly alongside channels without third-party subscriptions.
- Granular permissions: Agencies compartmentalize client projects into dedicated teams and private channels with distinct membership lists and roles.
- Unrestricted search archives: Organizations retain indefinite access to conversational history and code snippets without cloud message expiration limits.