> Slack has been... very slow to fix bugs / add new features. They're starting to feel like Microsoft... like they don't move fast, aren't trying to improve anything, and don't care about customer feedback.

we're looking for a self-hosted alternative. tried hipchat, and it was worse than slack in the areas you mentioned. mattermost has been a ray of sunshine, so far, relatively speaking. still testing it out, but they are super responsive to their users and community, between github, their forum, their pre-release server (https://pre-release.mattermost.com/core ), etc... they also seem to be aggressively adding new features and fixing bugs.

I realize I probably sound like a shill, but it just has been that much of a positive experience so far.