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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.

Slack employees working at the Slack office in
San Francisco, California, November 21st, 2014.

[Photo: Talia Herman, courtesy of Slack]

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.

Eighteen months later, it's clear Slack has staying power. The company is celebrating the first anniversary of its official release in both free and paid versions by releasing new stats on its usage which it says make it the fast-growing business app of all time:

  • 500,000 people now use Slack daily, including users in 60,000 teams
  • 135,000 of those people are paying for Slack, adding up to $12 million in annual revenue
  • Slack users send 300 million messages to each other a month
  • The average Slack user is connected for more than nine hours a day and spends more than two of those hours in active usage, such as reading and writing messages

Already, Slack had made headlines for the swiftness with which it reached a valuation of $1 billion, based on the $180 million in funding it's received so far.

Not bad for a product which got its start when Butterfield and his colleagues tried to launch a multi-player online game called Glitch. The game didn't take off—but its creators found the internal collaborative tools they'd built for themselves to be so useful that they thought it might be the basis of a business.

What they didn't know was how rapidly that business would grow. "We've blown past every estimate and prediction we made in the early days," says Butterfield. "It's consistently surprising."

Slack is still so new that most of the users coming on board are part of organizations which have just signed up for the service. But the evidence also suggests that the more an organization uses Slack, the more it gets out of it. "Existing teams grow something like 6% to 8% per month," Butterfield says.

Polish and Power

Slack provides organizations with chat rooms called channels, along with direct messaging for private conversations. For paying customers, every message gets saved indefinitely, creating an archive of the business's knowledge. There's nothing groundbreaking about that concept, which is similar to more venerable services such as HipChat.

But Slack stands out both for its user-friendliness and technical sophistication. For instance, integrations allow users to hook the service into other business tools, from Airbrake to Zendesk. They can allow Slack to index information stored outside its boundaries, such as in Dropbox folders, or to trigger automatic Slack messages when something gets added or changed in another service. Slack says that users have set up 800,000 of these integrations, which spawn 3 million messages a day.

Logically enough, technology-savvy companies have been particularly quick to adopt the service. "At this point, maybe the majority of venture-backed Bay Area tech startups use Slack," Butterfield says. "But it’s obviously interesting for us to get beyond that." He mentions an industrial-solvents manufacturer as an example of the sort of companies which are now buying into the vision.

As more companies outside of startup culture take notice of Slack, there are more instances of the adoption process moving at a less frenzied pace. "We have some teams where someone signs up and a week later we have 50 people using it every day," Butterfield says. "We have some teams where it takes a year."

For now, the service's growth remains dazzling: The number of active daily users has grown by 35% in 2015 alone. User signups are "pretty much staying active as a percentage," Butterfield says. "Each week we add more than we added the previous week."

The larger Slack gets, the harder it will get to maintain the same rate of growth. In the past six months, its user base has doubled twice; Butterfield says he expects the next doubling to take slightly longer. But the fact that he can reasonably talk about it doubling once again in the next few months suggests that Slack's boom times are far from over.

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