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Slack is a cloud-based team communication tool cofounded in 2013 by Canadian entrepreneur and now-CEO Stewart Butterfield. Slack was originally meant to be an internal communication tool at Butterfield's small company Tiny Speck, as his team developed the now-defunct online game Glitch. But by 2015, Slack had become a tech and media darling for its ease of use and fun in-app features. It works by offering communication over topic-based "channels" in the form of Internet relay chat that allows collaborators to tag each other in conversation, "star" responses, and even share files in the thread of a chat. It also offers private groups and direct message formats, as well as joyful features like a GIF-generating hack that pulls content from another playful company, Giphy, into a chat using a simple keyword text command. And Slack's growth is continuing at an exponential rate: In April 2015, Slack had 750,000 users. By the end of the year, it had close to 2 million and was valued at $2.8 billion. That's because Slack has succeeded where other collaboration platforms have failed: It makes company communication not just easy, but fun. Its elegantly designed chat rooms and intuitive interface allow for instant team communication, essentially eliminating the need for email chains. The app is even being hailed by some as the death of email at work. Indeed, teams using Slack (which include those from Pinterest, eBay, NASA, and the U.S. Department of State) report a 49% reduction in emails sent, and some companies are using Slack as a de facto content management system. The New York Times used it to live-blog a Republican debate leading up to the 2016 election. Individuals are creating channels for their friends and families, too. And Slack's open API means it integrates easily with other platforms like Gmail and even Uber--one more reason the platform is much more than an enterprise communication tool.

The company's competitive advantage in 2016:

It is now the fastest growing B2B application ever and is used by 2 million daily active users.

The biggest challenges standing in this company's way in 2016:

Possible new competition from social networking giant Facebook, which wants to launch a special version of its services for businesses in 2016 and has begun testing a workplace messaging app

What to look out for:

Possible IPO in the next year--the company recently kicked off an "IPO readiness" program

Social media handles:

Twitter: @SlackHQ

Diversity breakdown:

70% white
4% African American
19% Asian
7% Multiracial or other
39% women
18% of engineering team is female
10.3% identify as LGBTQ


Nearly $3 billion
public or private
$25-$30 million
Two million daily users worldwide; 570,000 of those are paid users
San Francisco, CA