Every feature you mention was available in the '90s. I'm not saying Slack is bad, just that it's nothing impressive or innovative. The only surprising thing about it is that someone didn't make it sooner.
Moreso that open source sprouts by necessity mostly. IRC buildbots and other integrations have been around forever. It's just that Slack paid for the integrations that really makes it shine. Money, and well the work->integrations it buys, really talks.
> Every feature you mention was available in the '90s.
The fact that you could log irc transcripts, index them, give them a web interface, and write bots to chain things together is not the same feature as Slack integrations. If that is your bar for a feature, then we might as well give up trying to write innovative software, because it all uses the same opcodes anyway.
> I'm not saying Slack is bad, just that it's nothing impressive or innovative.
The attitude that a new product is not innovative because its features resemble features from past products leads to no logical conclusion except that nothing is innovative. Everything is based on previous ideas.
If a product were merely the sum of its features, then Apple would not be alive today.
... is that not the hallmark of a great product?