Although it is nice to see an open source alternative, my team and I went through a period of trying out different chat services and passed over Slack and MM and went for Discord.

There is something to be said for hosting your own service and knowing exactly what is running, but we didnt have that specific use case. Our main desire was to have a much longer history than what the free tier of slack provided and the ability to have more restrictive channels.

Slack's message limit was a non-starter for us. Not because of the limit itself, but because it applied globally rather than per channel. Once we introduced a "random", screw-off channel, we started to see some of our slower, yet important channels completely lose their history.

Discord is designed more for gaming, but we've been able to use it extremely effectively and its nice to see it follow closely behind the feature additions of other chat services.

The best open source Slack alternative I've found is Matrix/Riot[1]. In fact, I much prefer it over Slack.

It even has federation, end to end encryption and voice calls.

[1]https://about.riot.im/

Since is advertised as "Open source, private cloud Slack-alternative"

My first question is: How can I import slack chat history, channels and user accounts?

I tried finding this info the landing page but I couldn't find it.

You can import teams and channels.

right, thanks, digging a bit more I found how.

https://docs.mattermost.com/administration/command-line-tool...