Slack (software)

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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; 5 years ago (2013-08)[2]
Stable release(s) [±]
iOS 3.48 / July 7, 2018; 2 months ago (2018-07-07)[3]
Android 2.63.0 / July 13, 2018; 2 months ago (2018-07-13)[4]
Windows 3.2.0 / June 5, 2018; 3 months ago (2018-06-05)[5][6]
macOS 3.2.0 / June 5, 2018; 3 months ago (2018-06-05)[7]
Linux 3.2.1 / May 31, 2018; 3 months ago (2018-05-31)[8]
Chrome OS (Discontinued) 1.0.3 / December 6, 2013; 4 years ago (2013-12-06)[9]
Windows Phone (Discontinued) 2016.913.0.0 / September 13, 2016; 2 years ago (2016-09-13)[10]
Written in Electron (C++, JavaScript, ECMAScript, etc.)[11]
Operating system Windows, macOS, Linux, iOS, Android, Windows Phone,[12] Commodore 64[13]
Type Collaborative software[14]
License Proprietary

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 his company, Tiny Speck, in the development of Glitch, a now defunct online game.[15][16] The name is an acronym for "Searchable Log of All Conversation and Knowledge".[17]


Slack was launched in August 2013.[18] In January 2015, Slack announced the acquisition of Screenhero.[19]

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.[20]

Slack used to offer compatibility with the non-proprietary IRC and XMPP messaging protocols, but announced in March 2018 that it would close the corresponding gateways by May 2018.[21]

In August 2018, Slack bought IP assets of Atlassian's two enterprise communications tools, HipChat and Stride.[22]


While no longer using an IRC backend, Slack offers many IRC-like features, including persistent chat rooms (channels) organized by topic, private groups and direct messaging.[16] All content inside Slack is searchable, including files, conversations, and people. On the free plan, only the 10,000 most recent messages can be viewed and searched.[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.


Slack integrates with a large number of third-party services and supports community-built integrations.[27] Major integrations include services such as Google Drive, Trello, Dropbox, Box, Heroku, IBM Bluemix, Crashlytics, GitHub, Runscope, Zendesk,[28][29] and Zapier.[30] In December 2015, Slack announced their app directory, consisting of over 150 integrations that users can install.[31] In March 2018, Slack announced its partnership with the financial and human capital management firm Workday; Adding to Slack's list of plugins. This integration allows Workday customers to access features from directly within the Slack interface.[32][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 2015 promotional video.[36]

Business model

Slack is a freemium product, whose main paid features are the ability to search more than 10,000 archived messages and add unlimited apps and integrations. They claim support for an unlimited number of users. When freeCodeCamp attempted to switch its community of over 8,000 users to Slack in 2015, however, they experienced many technical issues and were advised by Slack support to limit their channels to "no more than 1,000 users (ideally more like 500)".[37][38][needs update] That specific limit no longer applied by January 2017.[39]


The company originally raised nearly $43 million in April 2014.[40] 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.[41]

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 included Institutional Venture Partners, Horizons Ventures, Index Ventures and DST Global.[42] In April 2015, the company raised another $160 million.[43] In April 2016, the company announced that it had raised an additional $200 million in funding.[44]

On July 26, 2018, Atlassian announced the shutdown of its competing HipChat and Stride effective February 11, 2019, and the sale of their intellectual property to Slack. Slack will pay an undisclosed amount over three years to assume the user bases of the services, and Atlassian will take a minority investment in Slack. The companies also announced a commitment to work on integration of Slack with Atlassian services.[45][46]


8,000 customers signed up for the service within 24 hours of its launch in August 2013.[18][47] 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.[48][49] By April 2015, those numbers had grown to 200,000 paid subscribers and a total of 750,000 daily active users.[50] Late in 2015, Slack passed more than a million daily active users.[51][52] As of May 2018, Slack had over 8 million daily users, 3 million of whom had paid accounts.[53]

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.[54] 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".[55]

Slack was recognized as the best startup of the year 2017 at the 10th Crunchies Awards, organized by TechCrunch.[56]

The digital rights group Electronic Frontier Foundation (EFF) has cautioned that "Slack stores and is able to read all of your communications, as well as identifying information for everyone in your workspace".[57] While commending the company for "follow[ing] several best practices in standing up for users" concerning government data requests, such as requiring a warrant for content stored on its server, and awarding it four out of five stars in its 2017 "Who has your back" report[58], the EFF also criticized Slack for "a broad set of exceptions" to its promise to notify users of such requests, and for other privacy shortcomings.[57]


Slack has been criticized because the data is stored exclusively on cloud servers under Slack control.[59][60]


Open source

There are open source alternatives such as Rocket.Chat, Mattermost and Zulip that are free and can be self-hosted.[59]


Other alternatives to Slack that follow a similar business model are Flock and Ryver. Microsoft Teams,[61] Hangout Chats,[62] Tibco Tibbr are other alternatives.

See also


  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 7 July 2018. 
  4. ^ "Slack". Google Play. Google. Retrieved 8 July 2018. 
  5. ^ "Slack for Windows & Linux". Slack. Retrieved 26 July 2018. 
  6. ^ "Download Apps". Retrieved 28 September 2016. 
  7. ^ "Slack". Mac App Store. Apple Inc. Retrieved 26 July 2018. 
  8. ^ "Download Slack for Linux". Retrieved 27 July 2018. 
  9. ^ "Slack". Chrome Web Store. Google. Retrieved 28 September 2016. 
  10. ^ "Slack". Windows Store. Microsoft. Retrieved 28 July 2016. 
  11. ^ "Desktop Application Engineer". Archived from the original on 2015-09-13. Retrieved 2016-07-22. 
  12. ^ Slack, Slack apps for computers, phones & tablets, retrieved 2015-04-19 
  13. ^ Jeffrey Harris, Slack client for Commodore 64, retrieved 2016-11-29 
  14. ^ "Crunchbase - Slack Technologies". CrunchBase. Retrieved 2015-04-19. 
  15. ^ Tam, Donna, Flickr founder plans to kill company e-mails with Slack, retrieved 2013-11-26 
  16. ^ a b Thomas, Owen, Die, Email, Die! A Flickr Cofounder Aims To Cut Us All Some Slack, retrieved 2013-11-26 
  17. ^ Kim, Eugene (September 28, 2016). "Slack, the red hot $3.8 billion startup, has a hidden meaning behind its name". UK Business Insider. 
  18. ^ 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 
  19. ^ "Screenhero joins Slack". The Screenhero Blog. 
  20. ^ Greenberg, Andy (27 March 2015). "Slack Says It Was Hacked, Enables Two-Factor Authentication". Wired. Condé Nast. Retrieved 7 January 2016. 
  21. ^ "Slack cuts ties to IRC and XMPP, cos they don't speak Emoji". Retrieved 2018-03-18. 
  22. ^ "Slack forms key alliance as Atlassian throws in the towel on enterprise chat". TechCrunch. Retrieved 2018-08-17. 
  23. ^ "Message and storage limits on the Free plan". Slack Help Center. Retrieved 2018-03-18. 
  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. ^ Dowinton, Richard. "Bye Bye HipChat, Hello Slack!". Retrieved 2015-04-18. 
  28. ^ Gannes, Liz, Flickr Co-Founder Stewart Butterfield Turns to Workplace Communication Tools With Slack, retrieved 2013-11-26 
  29. ^ Augustine, Ann, Slack Sets New Standard for Team Communication Online, retrieved 2013-11-27 
  30. ^ Zapier. "Zapier | The easiest way to automate your work". Zapier. Retrieved 2018-02-20. 
  31. ^ "Slack launches an app store and an $80 million fund to invest in new integrations". The Verge. Retrieved 2016-02-22. 
  32. ^ "Workday and Slack announce partnership; Google, Microsoft and Facebook on the horizon". IT Business. Retrieved 2018-03-29. 
  33. ^ "Industry Leaders Slack & Workday are Now Partners". Retrieved 2018-03-29. 
  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. ^ "So Yeah We Tried Slack… and We Deeply Regretted It". 2015-06-21. Retrieved 2017-03-19. 
  38. ^ "Startup founder claims $2.8 billion startup Slack is misleading people about its free 'unlimited' plan". 2015-06-22. Retrieved 2016-01-05. 
  39. ^ "Despite its marketing, Slack's free tier limits your total number of users". 2017-01-20. Retrieved 2018-07-19. 
  40. ^ Ingrid Lunden (25 April 2014). "Slack, Stewart Butterfield's Collaboration Software Startup, Has Raised $42.75M". Techcrunch. Retrieved 28 January 2015. 
  41. ^ Alex Hern (3 November 2014). "Why Slack is worth $1bn: it's trying to change how we work". The Guardian. Retrieved 28 January 2015. 
  42. ^ Macmillan, Douglas. "Slack's Valuation More Than Doubles to $2.8 Billion in Five Months". Wall Street Journal. Retrieved 28 March 2015. 
  43. ^ Ingrid Lunden (15 April 2015). "Used Daily By 750K Workers, Slack Raises $160M, Valuing Collaboration Startup At $2.8B". Techcrunch. Retrieved 15 April 2015. 
  44. ^ "Slack is work chat's runaway train, raises $200M at $3.8B". TechCrunch. AOL. April 1, 2016. 
  45. ^ "Slack buys Hipchat with plans to shut it down and migrate users to its chat service". The Verge. Retrieved 2018-07-26. 
  46. ^ "Slack is buying, and shutting down, HipChat and Stride". TechCrunch. Retrieved 2018-07-26. 
  47. ^ Fingas, Jon, Flickr creator takes sign-ups for Slack, an office collaboration tool with universal search, retrieved 2013-11-26 
  48. ^ "Slack growth skyrockets: 10,000 new active users each week". Fortune. Retrieved 2015-06-07. 
  49. ^ "Billion-dollar startup Slack says it's adding $1 million in new contracts every 11 days". Business Insider. Retrieved 2015-06-07. 
  50. ^ "Slack continues huge growth, is now valued at $2.8 billion". The Verge. Retrieved 2015-06-07. 
  51. ^ "Slack Keeps On Growing". MIT Technology Review. Retrieved 2015-06-25. 
  52. ^ "Slack launches user groups, hits 1.7M daily active users and 470K paid seats". VentureBeat. Retrieved 2015-10-30. 
  53. ^ Newton, Casey (2018-05-23). "Slack adds action buttons to become a true workplace communication hub". The Verge. Retrieved 2018-05-23. 
  54. ^ "Slack: workplace message app so cute you want to use it at home". Financial Times. March 25, 2015. (subscription required)
  55. ^ Fischer, Molly (May 17, 2017). "Select/all: What Happens When Work Becomes a Nonstop Chat Room". New York magazine. Retrieved 2017-05-23. 
  56. ^ Lardinois, Frederic. "And the winners of the 10th Annual Crunchies are…". TechCrunch. 
  57. ^ a b Cohn, Cindy; Gebhart, Gennie (2018-02-14). "The Revolution and Slack". Electronic Frontier Foundation. Retrieved 2018-03-18. 
  58. ^ "Who Has Your Back? Government Data Requests 2017". Electronic Frontier Foundation. 2017-07-10. Retrieved 2018-03-18. 
  59. ^ a b Finley, Klint (March 16, 2016). "Open sourcers race to build better versions of Slack". Wired. Retrieved 2017-07-25. 
  60. ^ 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. 
  61. ^ Finnegan, Matthew. "Microsoft Teams: Its features, how it compares to Slack and other rivals". Computerworld. Retrieved 2018-08-13. 
  62. ^ "Google's Slack alternative is available starting today". Engadget. Retrieved 2018-08-13. 

External links

  • Official website
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