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Slack is a cloud-based set of proprietary team collaboration tools and services, founded by Stewart Butterfield.[1] Slack began as an internal tool used by their company, Tiny Speck, in the development of Glitch, a now defunct online game.[14][15] The name is an acronym for "Searchable Log of All Conversation and Knowledge".[16]

Slack Technologies Logo.svg
Original author(s) Stewart Butterfield, Eric Costello, Cal Henderson, and Serguei Mourachov[1]
Developer(s) Slack Technologies
Initial release August 2013; 4 years ago (2013-08)[2]
Stable release(s) [±]
iOS 3.28 / September 12, 2017; 5 months ago (2017-09-12)[3]
Android 2.45.0 / October 6, 2017; 4 months ago (2017-10-06)[4]
Windows 2.2.1 / September 17, 2016; 16 months ago (2016-09-17)[5][6]
macOS 2.8 / September 12, 2017; 5 months ago (2017-09-12)[7]
Chrome OS 1.0.3 / December 6, 2013; 4 years ago (2013-12-06)[8]
Windows Phone 2016.913.0.0 / September 13, 2016; 16 months ago (2016-09-13)[9]
Written in Electron (C++, JavaScript, ECMAScript, etc.)[10]
Operating system Windows, macOS, Linux, iOS, Android, Windows Phone,[11] Commodore 64[12]
Type Collaborative software[13]
License Proprietary



Slack was launched in August 2013.[17] In January 2015, Slack announced the acquisition of Screenhero.[18]

In March 2015, Slack announced that it had been hacked over the course of four days in February 2015, and that some number of users’ data was compromised. That data included email addresses, usernames, hashed passwords, and, in some cases, phone numbers and Skype IDs that users had associated with their accounts. In response, Slack added two-factor authentication to their service.[19]


While no longer using an IRC backend, Slack offers a lot of IRC-like features: persistent chat rooms (channels) organized by topic, as well as private groups and direct messaging (again, historically based on IRC).[15] All content inside Slack is searchable, including files, conversations, and people. Slack integrates with a large number of third-party services and supports community-built integrations.[20] Major integrations include services such as Google Drive, Trello, Dropbox, Box, Heroku, IBM Bluemix, Crashlytics, GitHub, Runscope and Zendesk.[21][22] In December 2015, Slack announced their app directory, consisting of over 150 integrations that users can install.[23] Users can add emoji buttons to their messages, which other users can then click on to express their reactions to messages.[24]


Slack teams allow communities, groups, or teams to join through a specific URL or invitation sent by a team admin or owner. Although Slack was meant for organizational communication, it has been slowly turning into a community platform, a function for which users had previously used message boards or social media such as Facebook or LinkedIn groups.[25] Many of these communities are categorized by topics which a group of people may be interested in discussing.


Public channels allow team members to communicate without the use of email or group SMS (texting). They are open to everyone in the chat provided they have first been invited to join the client. Private channels allow for private conversation between smaller sects of the overall group. These can be used to break up large teams into their own respective projects. Direct messages allow users to send private messages to a specific user rather than a group of people.[26] Direct messages can include up to nine people (the originator plus eight people). Once started this direct message group can be converted to a private channel.

Business modelEdit

Slack advertises itself as a freemium product available for an unlimited number of users, but it was reported by Quincy Larson[27] that the limit is actually 8,462 users per channel. Users can upgrade to various paid versions to gain access to larger channels, or additional features.[28]


The company originally raised nearly $43 million in April 2014.[29] In October 2014, the company raised $120 million in venture capital with a $1.2 billion valuation led by Kleiner Perkins Caufield & Byers and Google Ventures. Earlier investors Andreessen Horowitz, Accel Partners and The Social+Capital Partnership also participated in this round.[30]

In March 2015, Slack signed a deal with investors to raise up to $160 million in a funding round that valued the company at $2.76 billion. New investors include Institutional Venture Partners, Horizons Ventures, Index Ventures and DST Global.[31] In April 2015, the company raised another $160 million.[32] In April 2016, the company announced that it had raised an additional $200 million in funding.[33]


Slack provides mobile apps for iOS, Android, and Windows Phone (beta),[34] in addition to their web browser client and electron desktop clients for macOS, Windows, and Linux (beta). Slack is also available for the Apple Watch, allowing users to send direct messages, see mentions, and make simple replies.[35] It was featured on the home screen of the Apple Watch in a promotional video.[36]


8,000 customers signed up for the service within 24 hours of its launch in August 2013.[17][37] In February 2015, the company wrote that around 10,000 new daily active users were signing up each week, and had more than 135,000 paying customers spread across 60,000 teams.[38][39] By April, those numbers had grown to 200,000 paid subscribers and a total of 750,000 daily active users.[40] In 2015, Slack passed more than a million daily active users.[41][42]

The Financial Times wrote in March 2015 that Slack was the first business technology to have crossed from business into personal use since Microsoft Office and the BlackBerry.[43] In 2017 a writer at New York magazine described it as "a compulsion, a distraction[, a] burden ... another utility we both rely on and resent".[44]

Slack was recognized as the best startup of the year 2017 at the 10th Crunchies Awards, organized by TechCrunch.[45]


Slack has been criticized because the data is stored exclusively on cloud servers under Slack control.[46][47] There are now open source alternatives, such as Rocket.Chat and Mattermost that are free and can be self-hosted.[46]

See alsoEdit


  1. ^ a b Kumparak, Greg (February 5, 2015). "Slack's Co-Founders Take Home The Crunchie For Founder Of The Year". TechCrunch. Retrieved 2015-04-10. 
  2. ^ Zax, David, Flickr Cofounders Launch Slack, An Email Killer, retrieved 2015-04-19 
  3. ^ "Slack - Team Communication". App Store. Apple Inc. Retrieved 28 September 2016. 
  4. ^ "Slack". Google Play. Google. Retrieved 6 September 2017. 
  5. ^ "Slack for Windows & Linux". Twitter. Retrieved 28 September 2016. 
  6. ^ "Download Apps". Retrieved 28 September 2016. 
  7. ^ "Slack". Mac App Store. Apple Inc. Retrieved 28 September 2016. 
  8. ^ "Slack". Chrome Web Store. Google. Retrieved 28 September 2016. 
  9. ^ "Slack". Windows Store. Microsoft. Retrieved 28 July 2016. 
  10. ^ "Desktop Application Engineer". Archived from the original on 2015-09-13. Retrieved 2016-07-22. 
  11. ^ Slack, Slack apps for computers, phones & tablets, retrieved 2015-04-19 
  12. ^ Jeffrey Harris, Slack client for Commodore 64, retrieved 2016-11-29 
  13. ^ "Crunchbase - Slack Technologies". CrunchBase. Retrieved 2015-04-19. 
  14. ^ Tam, Donna, Flickr founder plans to kill company e-mails with Slack, retrieved 2013-11-26 
  15. ^ a b Thomas, Owen, Die, Email, Die! A Flickr Cofounder Aims To Cut Us All Some Slack, retrieved 2013-11-26 
  16. ^ Kim, Eugene (September 28, 2016). "Slack, the red hot $3.8 billion startup, has a hidden meaning behind its name". UK Business Insider. 
  17. ^ a b Koetsier, John (15 August 2013), "Flickr founder Stewart Butterfield's new Slack signed up 8,000 companies in 24 hours", VentureBeat, retrieved 7 January 2016 
  18. ^ "Screenhero joins Slack". The Screenhero Blog. 
  19. ^ Greenberg, Andy (27 March 2015). "Slack Says It Was Hacked, Enables Two-Factor Authentication". Wired. Condé Nast. Retrieved 7 January 2016. 
  20. ^ Dowinton, Richard. "Bye Bye HipChat, Hello Slack!". Retrieved 2015-04-18. 
  21. ^ Gannes, Liz, Flickr Co-Founder Stewart Butterfield Turns to Workplace Communication Tools With Slack, retrieved 2013-11-26 
  22. ^ Augustine, Ann, Slack Sets New Standard for Team Communication Online, retrieved 2013-11-27 
  23. ^ "Slack launches an app store and an $80 million fund to invest in new integrations". The Verge. Retrieved 2016-02-22. 
  24. ^ Crook, Jordan. "Slack Adds Emoji Reactions". 
  25. ^ "Why Slack is Exploding (as a Community-Building Platform)". 2015-07-08. Retrieved 2016-01-05. 
  26. ^ Slack. "Slack: Be less busy". Slack. Retrieved 2016-03-16. 
  27. ^ "So Yeah We Tried Slack… and We Deeply Regretted It". 2015-06-21. Retrieved 2017-03-19. 
  28. ^ "Startup founder claims $2.8 billion startup Slack is misleading people about its free 'unlimited' plan". 2015-06-22. Retrieved 2016-01-05. 
  29. ^ Ingrid Lunden (25 April 2014). "Slack, Stewart Butterfield's Collaboration Software Startup, Has Raised $42.75M". Techcrunch. Retrieved 28 January 2015. 
  30. ^ Alex Hern (3 November 2014). "Why Slack is worth $1bn: it's trying to change how we work". The Guardian. Retrieved 28 January 2015. 
  31. ^ Macmillan, Douglas. "Slack's Valuation More Than Doubles to $2.8 Billion in Five Months". Wall Street Journal. Retrieved 28 March 2015. 
  32. ^ Ingrid Lunden (15 April 2015). "Used Daily By 750K Workers, Slack Raises $160M, Valuing Collaboration Startup At $2.8B". Techcrunch. Retrieved 15 April 2015. 
  33. ^ "Slack is work chat's runaway train, raises $200M at $3.8B". TechCrunch. AOL. April 1, 2016. 
  34. ^ "Slack for Windows Phone app beta appears to be available for everyone". Windows Central. 
  35. ^ "Slack brings its app to the Apple Watch (video) - VentureBeat - Mobile - by Jordan Novet". VentureBeat. 
  36. ^ Julie Bort (March 9, 2015). "Salesforce, Evernote, Slack, and other Apple Watch business apps - Business Insider". Business Insider. 
  37. ^ Fingas, Jon, Flickr creator takes sign-ups for Slack, an office collaboration tool with universal search, retrieved 2013-11-26 
  38. ^ "Slack growth skyrockets: 10,000 new active users each week". Fortune. Retrieved 2015-06-07. 
  39. ^ "Billion-dollar startup Slack says it's adding $1 million in new contracts every 11 days". Business Insider. Retrieved 2015-06-07. 
  40. ^ "Slack continues huge growth, is now valued at $2.8 billion". The Verge. Retrieved 2015-06-07. 
  41. ^ "Slack Keeps On Growing". MIT Technology Review. Retrieved 2015-06-25. 
  42. ^ "Slack launches user groups, hits 1.7M daily active users and 470K paid seats". VentureBeat. Retrieved 2015-10-30. 
  43. ^ "Slack: workplace message app so cute you want to use it at home". Financial Times. March 25, 2015. (subscription required)
  44. ^ Fischer, Molly (May 17, 2017). "Select/all: What Happens When Work Becomes a Nonstop Chat Room". New York magazine. Retrieved 2017-05-23. 
  45. ^ Lardinois, Frederic. "And the winners of the 10th Annual Crunchies are…". TechCrunch. 
  46. ^ a b Finley, Klint (March 16, 2016). "Open sourcers race to build better versions of Slack". Wired. Retrieved 2017-07-25. 
  47. ^ Peterson, Becky (July 26, 2017). "Uber didn't like Silicon Valley's biggest chat apps — so it was forced to make its own". Business Insider. Retrieved 2017-08-18. 

External linksEdit