Installed Mattermost, a Slack alternative, for work just before lockdown started. Pretty good, all things considered. A few surprisingly missing features, e.g. tagging groups, but easy to get going and (so far) to administrate. https://mattermost.com/
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@tejrnz While mattermost is open, it's open core. Please also take a look at matrix/riot: https://www.troopmessenger.com/blogs/mattermost-vs-matrix
