I’m an open source devotee, contributor, etc., but FOSS dropped the ball on this. Slack is IRC via the web, though it has a lot more bells and whistles.
As a business tool, it’s lightweight, flexible, extensible, and cheap. I work for a 100% remote company. We have a product, and we provides 365/24 support.
Internally, we use Slack as as you’d expect for regular conversation segregated by topic (e.g. general, random, development, support, etc.). We also have bot channels for notifications: code reviews (someone opens a PR), Trello, deployment progress (inc. code quality, test coverage, etc.), daemon errors (multiple servers), etc.
We’re tiny, and trying to cover all of that manually would take a lot of time. Not hard work. Just time.
Where Slack really starts to shine is having shared channels with our customers. Those sit right next to the others all on one page. Ditto direct message channels for individuals (both internal and customers). Even though I’m dealing with Big Co’s, I rarely see more than a couple of emails a week from them. I open email first thing and perhaps after lunch. That’s a significant change from only a couple of years ago.
I still use IRC. I have textual open and use it for a bunch of things. For now, Slack is eating everyone’s lunch, and when you lean on it heavily, as we do, it’s easy to see why.