Slack became a $2.8 billion company in less than two years - and it's showing no signs of slowing down

Slack, the wildly popular business messaging app, reached a $2.8 billion valuation in less than two years - and it's showing no signs of slowing down.

The company told us it now has 1.7 million daily active users, nearly a 55% growth from just four months ago when it had about 1.1 million daily active users.

That's pretty impressive when you break it down by days - roughly 5,000 new active users added each passing day. With that kind of growth, it's not hard to see the company's revenue growing even faster than it did in February, when it announced it's adding $1 million in new contracts every 11 days.

And all those users are also turning out to be pretty heavy users too. On Monday, the company celebrated a new milestone of seeing one million concurrent users - that is, one million out of the 1.7 million daily active users were connected to Slack at the exact same time. 

Slack declined to say at what time or for how long the one million users were seen concurrently (its spokeswoman only told us, "No small feat and something they keep an eye on internally"). No less, the company seems to have thrown a small party to celebrate the new record, as seen in this tweet by Slack CEO Stewart Butterfield: