Mattermost is an open-source, self-hostable online chat service with file sharing, search, and third party application integrations.

It is designed as an internal chat for organisations and companies, and mostly markets itself as an open-source alternative to Slack[6][7] and Microsoft Teams.

The code was originally proprietary, as Mattermost was used as an internal chat tool inside SpinPunch, a game developer studio, but was later open-sourced.

The company generates funds by selling support services and additional features that are not in the open-source edition.

[10][11][12][13] Aside from the in-browser version, there are desktop clients for Windows, MacOS and Linux and mobile apps for iOS and Android.