Slack has a very simple concept that resonates with many: IRC for the enterprise, with hooks between the chat app and just about any external service you can imagine. We already knew it was hot.
Now, thanks to momentum numbers released today -- Slack's first anniversary -- we know just how hot.
To wit: Slack reported that it has 500,000 daily users, with 135,000 paid accounts generating $12 million in annual revenue. At is current rate of growth, that breaks down to adding $1 million in annual revenue every 11 days. In the first six weeks of 2015 alone, Slack grew its business 135 percent.