Mattermost

Mattermost is an open-source collaboration platform built for organisations with demanding security and control requirements. It provides team messaging with channels, threads, direct messages, file sharing, voice calls and screen sharing, along with workflow tools, and can be deployed on infrastructure the customer controls. Its market is distinct from consumer-friendly chat tools. Defence organisations, government agencies, critical infrastructure operators, financial institutions and security-conscious technology companies often cannot put sensitive communications on a multi-tenant cloud service. Mattermost can be self-hosted in private clouds, on-premises data centres and even air-gapped networks without internet access, with features such as granular permissions, compliance exports, data retention policies, audit logs and high availability. Beyond chat, Mattermost focuses on mission-critical work. Playbooks provide repeatable checklists and processes for incident response and operational procedures, boards support task tracking, and integrations connect to developer and security tools such as GitLab, GitHub, Jira and alerting systems. That makes it a common hub for DevSecOps teams and for operations centres coordinating responses in real time. AI features can be configured to use models running inside the customer's own environment, which matters when data cannot leave. The open-source core is free to self-host, while enterprise editions add advanced security, compliance and support. The trade-offs are the usual ones: self-hosting means operational responsibility, and the user experience and integration ecosystem are not as extensive as Slack's, which matters for organisations prioritising convenience over control. Alternatives include Slack and Microsoft Teams, the dominant cloud collaboration tools; Rocket.Chat, another open-source, self-hostable platform; Element, built on the Matrix protocol with end-to-end encryption and federation; Zulip, open source with topic-based threading; and Wire for encrypted enterprise messaging. Choose Mattermost when you need secure, self-hosted collaboration for sensitive or mission-critical work. Choose a cloud tool when convenience matters more than control.