https://mattermost.com/
https://mattermost.com/pricing/

https://github.com/mattermost
https://github.com/mattermost/desktop
https://github.com/mattermost/mattermost-webapp
https://github.com/mattermost/mattermost-server

https://developers.mattermost.com/contribute/
https://developers.mattermost.com/contribute/getting-started/
https://developers.mattermost.com/contribute/server/

https://docs.mattermost.com/about/integrations.html
https://developers.mattermost.com/integrate/getting-started/

https://mattermost.com/community/

https://mattermost.com/deploy/

https://docs.mattermost.com/guides/playbooks.html

https://api.mattermost.com/

whatsnew
6.x
https://mattermost.com/blog/mattermost-v6-0-is-now-available/
    https://www.opennet.ru/opennews/art.shtml?num=55969