With 500,000 Users, Slack Says It's The Fastest-Growing Business App Ever

The collaboration tool—which rose from the ashes of an unsuccessful game—is still expanding at a torrid pace.

In August 2013, the business messaging and search tool known as Slack started signing up users for its beta version. 8,000 companies created accounts in the first 24 hours. That was a promising number, but it said more about the general interest in such tools and the reputation of Slack CEO and cofounder Stewart Butterfield—also the co-creator of Flickr—than the service's long term prospects.

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