Mattermost is an open-source, self-hostable online chat service designed for internal chat within organizations and companies. It is an alternative to Slack and Microsoft Teams and provides features such as file sharing, search, and integrations. Mattermost was initially used as an internal chat tool inside SpinPunch, a game developer studio, but was later open-sourced. It was released on October 2, 2015, and is written in Go and JavaScript. Mattermost is available in 16 languages and is licensed under the MIT License for "Mattermost Team Edition" Linux binary server compiled by Mattermost, Inc., AGPLv3 for uncompiled Mattermost server source code, (Apache License 2.0 for Admin Tools and Configuration Files), and Apache License 2.0 for the rest. Mattermost is a secure collaboration platform that is fully integrated with the tools you love. It provides advanced compliance auditing and reporting, flexible on-prem and secure cloud deployment, and is designed for enterprise scalability. Mattermost is open source and customizable, and it can be deployed in air-gapped networks and BYOD environments. It also provides cloud-neutral and self-host deployment options. Mattermost is available on Google Play and has over 500K downloads. It requires Mattermost Server v7.8.0+ to avoid incompatibilities and crashes. The primary source for core development on the Mattermost platform is available on GitHub.

Citations: [1] https://en.wikipedia.org/wiki/Mattermost [2] https://play.google.com/store/apps/details?gl=US&hl=en_US&id=com.mattermost.rn [3] https://youtube.com/channel/UCNR05H72hi692y01bWaFXNA [4] https://mattermost.com [5] https://github.com/mattermost/mattermost [6] https://vsupalov.com/docker-latest-tag/