Mattermost
Self-hostable team chat with full markdown message formatting.
Mattermost is an open-source team collaboration platform — a self-hostable alternative to Slack — whose messages support genuine markdown: headings, tables, blockquotes, task lists, and syntax-highlighted code blocks.
That fuller markdown support (Slack only offers a subset) plus on-premise deployment makes it common in engineering and security-sensitive organizations.
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Try markdown before you install anything
The free online markdown editor gives you a live side-by-side preview in the browser — a quick way to test the syntax Mattermost uses, with nothing to download or sign up for.
Open the editor