[bitexploder]

I don't think it is fair to classify them as just a "fancy IRC". I see technical people myself included think of them that way, but why isn't a slightly fancier IRC dominant?

Seamless mobile clients, integrations, animated gifs, etc. Slack has a lot of small but very sticky features.

[majewsky]

Exactly. My workplace is currently evaluating Slack and Microsoft Teams vs. "bolt on chat to the existing internal social network". I'm presently trying to figure out how to explain to the engineers running the evaluation that the value of Slack cannot must be understood by the quality of execution, not just as the sum of its features.

"How will we get people to use Slack if it does not have $feature [1]?" - "But hundreds of people are already using it, so your point is moot."

[1] e.g. SSO integration