[mattmanser]

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.