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Stewart Butterfield, co-founder and chief executive office of Slack. Ian Allen for TIME

How E-Mail Killer Slack Will Change the Future of Work

People ask two questions about Slack, the interoffice chat software used by some of the world's most closely watched companies. The first is whether the 21-month-old startup is actually worth its $2.8 billion valuation. The second is whether Slack is changing how much of the world works.

The first question is easier to answer. Even in an economy that has minted at least 65 new startups valued at $1 billion since January, Slack is growing fast. More than 1.7 million people have become daily users of the service since it was first released in February 2014; there were 10 times as many people using Slack in August of this year as there were during the same time last year. Venture-capital darlings Airbnb, BuzzFeed and Blue Bottle Coffee use it. So do Fortune 500 firms like Comcast and Walmart. Teams at NASA and the State Department are on Slack. (More than 2,000 people use Slack at Time Inc., which publishes this magazine and many others.) Not in a generation has a new tool been adopted more quickly by a wider variety of businesses or with such joy.

If you've used Facebook or Twitter, you'll understand why Slack is hot. The program--it's not that different from the instant messengers that were popular on the early Internet--helps different parts of a company communicate in real time. Slack preserves every comment in one easily searchable archive, and all those messages now skip your dreaded inbox. Slack's users, on average, spend 10 hours each weekday plugged into the application, which means for those who are already on it, getting work done increasingly looks like being in Slack.

Slack CEO Stewart Butterfield, 42, says this makes the firm worth much more than its current valuation. He wants his business to exceed Facebook's. (The social network's revenue in 2014 was $12.5 billion. Slack's is on track to hit $45 million this year.) Butterfield also wants Slack to do for the next decade what Microsoft did for the past two by dominating how millions work. That won't be easy. "We have grown so fast," he says. "Every time we figure out the best way to do something, it becomes obsolete."

There is something of a gold rush today for companies making not terribly sexy but potentially lucrative office software adapted to the way people work now--from their smartphones, around the clock, passing information back and forth through the cloud. Around the globe, companies will spend more than $3 trillion on information technology this year, according to research firm Gartner. Nearly 1 out of 10 of those dollars is being spent on software like Slack.

Which brings us to the second, harder question: Is Slack changing work, or is Slack exploding because work is changing? For centuries--from steam engines to elevators, typewriters to telephones--technology has transformed where we work and how, the consequences rippling through the rest of our lives. If you look at it one way, crediting Slack with what a human-genome researcher uncovers or an astronomer finds is like crediting Steve Wozniak's garage with creating the Apple I. And yet how much and how fast work is about to be transformed is in the hands of people like Butterfield. If you work in an office, history shows you may not like what comes next.

Sitting in a conference room in Slack's San Francisco office, it's fun to talk to Butterfield. Ask him what's wrong with how people work today and he'll say, "Well, let's go back to ancient Rome," and free-associate from there. Ask him about Siri and Butterfield may call Apple's robotic personal assistant "f-cking idiotic." Says Cal Henderson, Butterfield's longtime friend and Slack's co-founder and chief technology officer, "He's like an annoying, small, little ginger man."

This quirkiness begins to make some sense when you learn Butterfield was raised on a commune in Lund, British Columbia. His family got running water when he was 4, electricity when he was 5 and a computer when he was 7, after moving to Vancouver for school. At 12, he legally changed his given name, Dharma Jeremy, to Stewart.

After studying philosophy at Cambridge, he became captivated with the possibilities of the Internet, eventually trying, with his then wife Caterina Fake, to create a "strange and absurdist" video game called Game Neverending. It was never released, but by 2004 they had repurposed some of their software into what became the massively popular photo-sharing service Flickr.

In 2005, Yahoo acquired Flickr for a reported $25 million, a decision that Butterfield came to regret. Three years later, he quit, writing one of Silicon Valley's most shared farewell notes. "Please accept my resignation," the email read. "And I don't need no fancy parties or gold watches ... I will be spending more time with my family, tending to my small but growing alpaca herd and of course getting back to working with tin, my first love."

A year later, Butterfield launched another company and was back serenading colleagues with one of his ukuleles and trying to make another video game. Again he failed. But his outfit had built a chat tool for the company's first eight employees and decided to make a go with that. Because it helped them communicate with less tension, they called it Slack. It launched not long after.

Work on Slack for a few days and you can see why people think it can kill the most dreaded form of communication: email. Office workers send or receive 122 emails from the average company email account every day, according to the Radicati Group, a research firm. If for the sake of argument, if not reality, you assume a 9-to-5 shift, that's a new piece of incoming or outgoing mail every four minutes. It is no wonder that Hillary Clinton, owner of the country's most scrutinized inbox, once asked an aide for a copy of Send: Why People Email So Badly and How to Do It Better.

A large part of what makes Slack better than email is how fluid its conversations are. The program--for which companies pay $6.67 to $12.50 per month per user--allows different parts of a business to set up different channels for discussions. In this channel, the information technology group talks. In that channel, marketing meets. Anytime someone wants to alert you to something, he or she tags your name to a message, just as on Facebook. You can follow your colleagues' exchanges in real time, or you can come back to that conversation later.

Slack's makers say this kind of software enables transparency. If you are not copied on an email or not included in a meeting, you might not have a clue why a decision was made. This can breed resentment and confusion. Slack lets people who might have been forgotten or ignored look back and see why or how something happened. "The current modes of communication are outdated, and there's an opportunity for a new thing," says John O'Farrell, a Slack board member and partner at the venture-capital firm Andreessen Horowitz.

That's what's happening at Weaver Street Market, a North Carolina grocery chain, where workers check touch-screen computers running Slack to find out the latest on strawberry shipments, for instance. At the Philadelphia-based Tonic Design, Slack helped new co-workers get to know one another quickly after a recent merger. And at Hendricks Automotive, employees have been able to move as far away as Canada and Turkey while staying connected to colleagues back in Charlotte, N.C.

No doubt because it knows this increased connection can make people feel tethered to their jobs, Slack says it wants to tackle how much we work. The company is developing a do-not-disturb feature. People won't be interrupted by messages between, say, the hours of 10 p.m. and 8 a.m., in whatever time zone they live in. If you truly feel compelled to send someone a note during another person's off hours, the message won't appear in that colleague's Slack account until his or her do-not-disturb hours have ended.

Butterfield worries about this more than you might think. "I think that we're as a species not quite equipped to deal with the power of this stuff just in the same way we weren't quite equipped to deal with infinite free calories. This is how people end up with diabetes," he says. "We will now have the cognitive emotional diabetes of overinteracting with people who aren't physically present."

One solution may be to take people out of the equation. This is where Slack's robots come in. These pieces of automated software can respond to simple questions about when a meeting is scheduled or what's for lunch in the company cafeteria. At Polyvore, the e-commerce site recently acquired by Yahoo, bots periodically report back to employees on company financials. At the New York Times, engineers have built a bot that predicts for its editors what stories will perform best with readers on social media. "You can add them to your team and then they sit there and they're like a team member," says April Underwood, Slack's head of platform. Someday, as artificial intelligence improves, they may also fill out your expense reports or calculate next year's budget.

Anyone spotting the new, new thing that will change how we work forever has to do so knowing that history will likely make him look dumb. When advertising savant Jay Chiat suddenly (and very publicly) banished his workers from their desks in the 1990s, it looked like the day had dawned when the office as we know it was headed for the dustbin.

But eventually Chiat's workers got their offices back. (A lot of them were using their car trunks to store files.) And now 20 years later, a company like WeWork, an office-space provider, is valued at $10 billion. People like real offices and a permanent place to work after all.

You might call this the workplace-uncertainty principle: Every new tool adopted by office workers, no matter how valuable, has unintended consequences. For every upside, there's plenty of down. Think about popular open-office plans. Research has shown they increase stress and lower motivation. Or consider PowerPoint, Microsoft's ubiquitous presentation software, which in the past 25 years has become the standard way for millions of workers to communicate their ideas. That doesn't mean it's always the best way. Most famously, statistician Edward Tufte convinced NASA that a poor PowerPoint presentation on debris impact was one cause of the 2003 Space Shuttle Columbia explosion. Just because everyone is using one form of communication doesn't mean it's the right one for every conversation.

Take Slack's searchable archive, for example. Most office workers would be distressed to learn that their bosses are recording their every conversation. Now, with Slack, employees do that for their managers themselves. And that can create problems as workers leave a record of chatter they may regret. "We would like to get to the point where no one gets fired for using Slack," Butterfield says.

Slack also creates a setting that is much less buttoned-up than your typical corporate environment. Conversations have a tendency to look like text messaging or exchanges on newer social-media platforms such as Snapchat and WhatsApp. In practice this can become a rapid-fire exchange of animated GIFs and YouTube videos. (Bots can also be programmed to tell their own jokes.) Regardless of whether or not this constitutes "professional" communication, it may alienate older workers not well versed in expression through emojis.

And it can be distracting. "Slack is fun," says Michael Pryor, CEO of Trello, a company whose task-management software is popular with Slack users. Pryor says Slack can lead people to believe they are working when they are not. "A lot of time people can get sucked into this idea of reading every chat room and scanning things and reading around, but that's just distraction," he says. "You might as well be on Reddit." Talking about work is not necessarily productive.

Technology changes the way we talk to each other. That changes who we are. Slack helps text-based communication replace face-to-face interaction. In her new book, Reclaiming Conversation: The Power of Talk in a Digital Age, media scholar Sherry Turkle cautions against the dangers of this transformation. Research shows, she says, that empathy is lost when we privilege connectivity over conversation. Slack and technology like it quicken that development in many workplaces.

Tools like Slack also help make our transient workforce possible. Software company Intuit predicts that by the year 2020, freelancers, temporary workers, day laborers and independent contractors will constitute 40% of the American workforce. Having a tool that seamlessly preserves resources and instantly connects you with your temporary co-workers and short-term boss will ease that transition. Many of us won't have the 401(k) or the gold watch that was once the reward of a long career spent in the tin mines of our choosing. But we will have Slack--or something very much like it.

Even Butterfield says he cannot predict what Slack may be doing to us. But we know from history that it isn't likely to turn out how most people expect. Take perhaps the most recognizable workplace invention of the past century. In 1964 designer Robert Propst introduced something called the "Action Office." People were overjoyed. "Revolution Hits the Office," the New York Post proclaimed. Anyone who's entered a business since knows what happened next. We thought we were getting a smarter, more collaborative way to work.

Instead, we got the cubicle.

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