I had some confusion with the install. It seems the Docker install is favored, but not using a lot of Docker stuff I went with the gitlab-omnibus install on Ubuntu 16.10.
It worked but I didn't feel especially comfortable with it, there were a number of steps. That's vague enough be useless and it could have just been my own ignorance. What is the suggested install if that isn't too basic of a question?
I also had issues with it not liking users sending rather large files but I believe that's an odd use case.
I would use it again but the simplicity of Slack (no setup and no management) won out for now.
Mattermost team here, would welcome any feedback on how we could improve.
Here's a demo of Mattermost features vs Slack as FYI: https://www.youtube.com/watch?v=AKqHWqrAgpk