Mattermost Self-Hosted Chat

Mattermost is an open-source, self-hostable team messaging platform designed for enterprise and government use, providing secure, compliant team collaboration as an alternative to Slack. Founded by Ian Tien and Corey Hulen in 2015, with over 32,000 stars as of 2026, Mattermost is used by the US Department of Defense, Intel, Samsung, and Nasdaq. Key features include: channels and messaging (public and private channels, direct messages, group messages, threaded replies with reaction emojis, and message editing with history), enterprise security (HIPAA compliance, SOC 2 compliance, end-to-end encryption for sensitive channels, data retention policies, and compliance export for regulatory requirements), deployment (single binary deployment, Docker, Kubernetes with Helm charts, and high-availability multi-server deployment), authentication (Active Directory and LDAP integration, SAML 2.0 SSO, OAuth 2.0, OpenID Connect, and multi-factor authentication), integrations (incoming and outgoing webhooks, slash commands, REST API v4, bot accounts, and over 700 pre-built integrations), workflow automation (Playbooks feature for incident response runbooks with automated checklists, status updates, and retrospective timelines), voice and video (built-in voice calls, Jitsi and Zoom integration, and screen sharing), file sharing (file upload with preview, configurable storage backend including local filesystem, Amazon S3, and MinIO), message moderation (content filtering, profanity detection, and message flagging with admin review), board (integrated project management with Kanban boards, cards, and task assignment), and accessibility (WCAG 2.1 AA compliance, keyboard navigation, and screen reader support).