Is Slack the fastest growing business app ever?

Slack co-founder and CEO Stewart Butterfield
David Paul Morris | Bloomberg | Getty Images
Slack co-founder and CEO Stewart Butterfield

On its first birthday, Slack is already a "unicorn," the term reserved for start-ups with a valuation $1 billion or more. Even more newsworthy is Slack's growth rate during the first year.

Over half a million daily active users earned Slack the title of "fastest-growing business app ever" in Forbes. The founder, Stewart Butterfield, attributed Slack's success to pouncing at the perfect time for the service, which provides an instant messaging specifically for work colleagues.

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Butterfield, who also founded Flickr, released Slack just on the heels of Blackberry and Apple's messenger systems. Since then, Slack has persuaded companies such as Wordpress.org, The New York Times and Al Jazeera to free themselves from endless work emails and move toward more natural conversation.

To see more of Slack's numbers, the full report at Forbes.com is here.