I'm the OP, it doesn't really matter which was the first, my point was that we've had plenty of new "categories" of software. And in reality many that are just like Slack.

In some ways Google Apps for Business is a really good example of a sort of "new category" of communication software. You could plugin apps online, rather than have to host it your self.

A bit of googling shows he's called Slack a "brand new category of software" many times before, but I'm not clear what he thinks it is.

Slack wasn't the first chat application either. The fact that it's a value add atop IRC is irrelevant, as Gmail is a value add atop IMAP.

Gmail's a bad comparison because it never had to make money directly - it was just there to help Google build and maintain their search monopoly by acting as another data source and shutting out competitors. Slack, on the other hand, needs to make money because chat is their only product.

Gmail is the overwhelming reason that businesses pay for Google Apps.

Yes and slack is not the first instant messaging program. /snarky quip about your age and IRC/

How many corporations use G suite for their email? How many roll their own email systems and use thunderbird?

To the average user, email is a proprietary non-federated system filled with tracking.

Sorry, I don't mean that as snark. Many people born after 2000 have known nothing but Gmail as email and are surprised to learn that other email systems/providers exist.

That's nothing unique to age. I regularly talk to people born before 1960 (and 1970, and 1980....) who don't know that email is separate from it being on a website (about the only difference is that they know of Yahoo Mail, Hotmail, etc)