Designed as an enterprise-grade Slack alternative, Mattermost provides chat channels, direct messages, file sharing, and audio/video calls. It offers extensive integration with DevOps tools (Git, Jira, etc.) and built-in “Playbooks” for incident response and workflow automation. Key differentiators include on-premises deployment options (so organizations keep complete data control) and a fully open-source codebase that can be customized and extended. Mattermost emphasizes “mission-critical” use cases: it is used by many public sector and infrastructure clients requiring high security and compliance. As such, it supports features like two-factor auth, compliance reporting, and clustered high-availability setups. The product was co-founded in 2015 by long-time open-source developers (including the original developers of GitLab) and is offered in both a free self-hosted edition and commercial subscription editions with support.