Bots to sit in channels to passively log; bots which act to send messages to people who are presently offline, at the time at which they come online again; and so on.
Adding a log to IRC isn't particularly innovative. Slack's value is almost entirely in its user engagement, not its technology.
Nor was it obvious that if someone put it together properly it would achieve commercial success. I was theoretically in the right place at the right time to have put together something like Slack at my job, but there was no desire to invest enough to do that and eventually the entire product was EOL'ed a couple of years before Slack was released, not just because the product itself was not doing well but the entire market segment was not doing well. Commercial IM products have not done well historically, because it was difficult to do enough better than the free stuff to get people to pay.
What Slack may demonstrate is that, indeed, there was a market there all along, it's just the activation energy was higher than almost anyone was prepared to pay.
The only "innovation" Slack provided was the UI, and that's textbook "bad startup idea", because of how easy it is for someone else to step into the space.
Slack didn't innovate, it simplified. I called it a "UI" simplification, but you can call it whatever you like. They didn't innovate on technology, and that's a dangerous place to build your startup, because someone like Microsoft can eat your lunch and there's nothing you can do about it.
It did indeed... implement them as pieces. The out-of-the-box experience for an IRC network does not look like Slack.
And the UI was a non-trivial component. Personally I'm in the segment who doesn't much care and for whom IRC is a fine amount of bandwidth... but a looooot of other people, including lots of people with money, want something more.
Slack is not "just IRC". The proof is that if it was, we wouldn't be talking about Slack, we'd be talking about IRC. We aren't.
Those people with money can easily be stolen out from under Slack, precisely because they didn't innovate, they simplified.
Slack is "just IRC", and the proof is that if it were more, there wouldn't be nearly as much competition in the space, with more people joining every month, it seems.
Not marketing, or features or UX - price was key for us.
I still hope Slack wins, but MS is a very serious threat. In the end its best for us, users - prices will drop, new features will be added, support will be awesome all thanks to competition.
Who gives a damn about innovative? It may have been obvious and simple, but if no one else is doing it well, and they do, sneering at it seems dumb. They made a good call, and are profiting from it.
Pings show up - if you desperately need phone notifications there are many apps/solutions to deal with that too. (but lets be real...nobody ~really~ wants notifications outside of work)