Mattermost is an open core, self-hosted collaboration platform for teams that need secure chat, workflow automation, voice calling, screen sharing, and AI integration while keeping the deployment under their own control.

What it is

Mattermost is an open core, self-hosted collaboration platform. It bundles chat, workflow automation, voice calling, screen sharing, and AI integration into one system. This repository is the primary source for core development on the platform. The codebase is written in Go and React, organised as a monorepo, and the server runs as a single Linux binary that relies on PostgreSQL. A new compiled version is released under an MIT license every month on the 16th. Native clients exist for Android, iOS, Windows PC, macOS, and Linux, alongside the web interface, with the React Native client code living in the same monorepo.

The concrete problem it solves is data ownership for teams whose conversations cannot leave their own infrastructure. The project positions itself as the open alternative to Slack, replacing a hosted third-party messaging service with an instance the operator deploys and controls. The README frames the target work as mission-critical: DevSecOps, incident resolution, and IT service desk. In those settings the chat history, incident timelines, and automation hooks sit on infrastructure the organisation owns rather than in a vendor's cloud.

Key capabilities

• Chat, workflow automation, voice calling, screen sharing, and AI integration in a single platform.
• Server delivered as a single Linux binary that relies on PostgreSQL for storage.
• Native mobile and desktop clients for Android, iOS, Windows PC, macOS, and Linux, plus the web interface.
• Integration surface for developers covering APIs, Webhooks, slash commands, Apps, and plugins.
• Monthly compiled release published under an MIT license on the 16th of each month.
• Monorepo layout spanning the Go server, the React web application, and the React Native clients.

Who uses it and how

• DevSecOps teams that run chat and automation on infrastructure they administer instead of a hosted service.
• Incident resolution teams that need a controlled place for responders to coordinate during an outage.
• IT service desk groups that route requests through the platform rather than an external SaaS tool.
• Operators deploying at different scales, from a single Docker container or Ubuntu 20.04 LTS host to Kubernetes and Helm clusters.
• Developers contributing to the server itself, supported by documented developer machine setup and the hacktoberfest topic on the repository.

Getting started

Self-host via Docker, Ubuntu, tar, Mattermost Omnibus, or Kubernetes with Helm, following the deployment guide for each path. A cloud sign-up is available to try the platform without installing anything.

How it compares

Mattermost positions itself as the open alternative to Slack, and the contrast is licence and hosting: Slack is a proprietary hosted service, while Mattermost ships an open core server plus compiled releases under an MIT license every month on the 16th. Self-hosting puts the message store in the operator's own PostgreSQL instance, so data ownership and the cost model follow from running the infrastructure rather than from a per-seat subscription to a third party.

When to use it — and when not to

A self-hoster must operate a Linux host with PostgreSQL and keep pace with the monthly release cadence. Teams that want a zero-operations hosted product, or that cannot staff database and server maintenance, should stay with a SaaS alternative. Note also that the repository metadata lists the license as NOASSERTION even though the README states compiled releases are MIT, so anyone with strict automated licence compliance requirements should verify the actual terms before adopting it.