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 releaseAugust 2013; 7 years ago (2013-08)[2]
Stable release(s) [±]
iOS20.12.10 / December 14, 2020; 2 months ago (2020-12-14)[3]
Android20.12.10 / December 14, 2020; 2 months ago (2020-12-14)[4]
Windows4.12.0 / December 14, 2020; 2 months ago (2020-12-14)[5]
macOS4.12.0 / December 14, 2020; 2 months ago (2020-12-14)[6]
Linux (Beta)4.12.0 / December 14, 2020; 2 months ago (2020-12-14)[7]
Written inElectron (C++, JavaScript, etc.)[8], Hack (backend)[9]
Operating systemMicrosoft Windows, macOS, Linux, iOS, Android, Windows Phone[10]
Available in8 languages[11]
List of languages
English (UK), English (US), French (France), German (Germany), Japanese, Portuguese (Brazil), Spanish (Latin America), Spanish (Spain)
TypeCollaborative software[12]

Slack is a proprietary business communication platform developed by American software company Slack Technologies. Slack offers many IRC-style features, including persistent chat rooms (channels) organized by topic, private groups, and direct messaging.


Slack began as an internal tool for Stewart Butterfield's company Tiny Speck during the development of Glitch, an online game.[13] Slack launched in August 2013.[14]

In March 2015, Slack announced it had been hacked over four days in February 2015, and that some data associated with user accounts had been compromised, including email addresses, usernames, hashed passwords, phone numbers, and Skype IDs. In response to the attacks, Slack added two-factor authentication to its service.[15]

Slack was previously compatible with non-proprietary Internet Relay Chat (IRC) and XMPP messaging protocols, but the company closed the corresponding gateways in May 2018.[16]

"Searchable Log of All Conversation and Knowledge" is a backronym for "Slack".[17]

On January 1, 2021, Slack and Salesforce announced an agreement for Salesforce to acquire Slack for a value of approximately $27.7 billion.[18]

On January 4, 2021, Slack suffered a large outage which lasted several hours. From 10 AM ET until 3 PM ET users could not log-in, send or receive messages, place or answer calls, and use Slack connections. After 3 PM, most of the core features became operational, except for push notifications, email, and third-party integrations including Google Calendar and Outlook Calendar.[19][20]


Slack offers many IRC-style features, including persistent chat rooms (channels) organized by topic, private groups, and direct messaging.[21] Content, including files, conversations, and people, is all searchable within Slack. Users can add emoji buttons to their messages, on which other users can then click to express their reactions to messages.[22][23]

Slack's free plan allows only the 10,000 most recent messages to be viewed and searched.[24]

On March 18, 2020, Slack redesigned its platform to simplify and customize the user experience.[25]


Slack teams allow communities, groups, or teams to join a "workspace" via a specific URL or invitation sent by a team admin or owner.[26] Although Slack was developed for professional and organizational communication, it has been adopted as a community platform, replacing message boards or social media groups.[23][27]


Public channels allow team members to communicate without the use of email or group SMS (texting). Public channels are open to everyone in the workspace.[28]

Private channels allow for private conversation between smaller sub-groups. These private channels can be used to organize large teams.[28]

Direct messages allow users to send private messages to specific users rather than a group of people. Direct messages can include up to nine people. Once started, a direct message group can be converted into a private channel.[23]


Slack integrates with many third-party services and supports community-built integrations, including Google Drive, Trello, Dropbox, Box, Heroku, IBM Bluemix, Crashlytics, GitHub, Runscope, Zendesk[29][30] and Zapier.[31] In December 2015, Slack launched their software application ("app") directory, consisting of over 150 integrations that users can install.[32]

In March 2018, Slack announced a partnership with financial and human capital management firm Workday. This integration allows Workday customers to access Workday features directly from the Slack interface.[33][34]


Slack provides an application programming interface (API) for users to create applications and automate processes, such as sending automatic notifications based on human input,[35] sending alerts on specified conditions, and automatically creating internal support tickets.[36] Slack's API has been noted for its compatibility with many types of applications, frameworks, and services.[35]


Slack provides mobile apps for iOS and Android in addition to their Web browser client and desktop clients for macOS, Windows (with versions available from the company's website and through the Windows Store),[37] and Linux (beta). Slack is also available for the Apple Watch, allowing users to send direct messages, see mentions, and make simple replies.[38] It was featured on the home screen of the Apple Watch in a 2015 promotional video.[39] Slack has been made to run on a Super Nintendo Entertainment System via Satellaview.[40][41]

Business model[edit]

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)".[42][43] That specific limit no longer applied by January 2017.[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, with Slack to assume the user bases of the services. The companies also announced a commitment to work on integration of Slack with Atlassian services.[45][46]

In July 2020, Slack acquired Rimeto, a startup company focused on directory building. This acquisition will provide additional search offerings of employees within a Slack workspace.[47][48]


8,000 customers signed up for the service within 24 hours of its launch in August 2013.[14][49] In February 2015, the company reported that approximately 10,000 new daily active users had signed up each week, and had more than 135,000 paying customers spread across 60,000 teams.[50][51] By April 2015, those numbers had grown to 200,000 paid subscribers and a total of 750,000 daily active users.[52] Late in 2015, Slack passed more than a million daily active users.[53][54] As of May 2018, Slack had over 8 million daily users, 3 million of whom had paid accounts.[55] At the time of its S-1 filing for IPO, dated April 26, 2019, Slack reported more than 10 million daily active users from more than 600,000 organizations, located in more than 150 countries.[56]

In March 2015, the Financial Times wrote that Slack was the first business technology to have crossed from business into personal use since Microsoft Office and the BlackBerry.[57] In 2017, New York magazine criticized the platform for being "another utility we both rely on and resent."[58]

In 2017, Slack was recognized as the best startup of the year at the Crunchies Awards, organized by TechCrunch.[59]

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".[60] 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,[61] 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.[60]


Slack has been criticized by users[62] for storing user data exclusively on cloud servers under Slack control.[63][64] This is found to be a particular issue for users with large teams, who experienced issues with connectivity within the app, access to archived messages, and the number of users for a given "workspace".[65]

Slack has additionally been criticized for a retroactive 2018 change to their privacy policy, allowing access to all public and private chat messages by workspace administrators, without the need of consent from any parties using the app.[66] According to the policy, Slack users would not be notified when their information is being accessed.[67]

See also[edit]


  1. ^ Kumparak, Greg (February 5, 2015). "Slack's Co-Founders Take Home The Crunchie For Founder Of The Year". TechCrunch.
  2. ^ Zax, David. "Flickr Cofounders Launch Slack, An Email Killer".
  3. ^ "Slack - Team Communication". App Store. Apple Inc. Retrieved December 30, 2020.
  4. ^ "Slack for Android - Release Notes". Slack. Retrieved December 30, 2020.
  5. ^ "Slack for Windows - Release Notes". Slack. Retrieved December 26, 2020.
  6. ^ "Slack". Mac App Store. Apple Inc. Retrieved December 30, 2020.
  7. ^ "Slack for Linux (Beta) - Release Notes". Retrieved December 30, 2020.
  8. ^ "Desktop Application Engineer". Slack. Archived from the original on September 13, 2015.
  9. ^ Sandler, Scott (April 14, 2020). "Hacklang at Slack: A Better PHP". Retrieved February 11, 2021.
  10. ^ Slack. "Slack apps for computers, phones & tablets".
  11. ^ "Manage your language preferences". Slack. Archived from the original on March 10, 2020. Retrieved March 10, 2020.
  12. ^ "Crunchbase - Slack Technologies". Crunchbase.
  13. ^ Tam, Donna. "Flickr founder plans to kill company e-mails with Slack". Retrieved October 13, 2018.
  14. ^ a b Koetsier, John (August 15, 2013). "Flickr founder Stewart Butterfield's new Slack signed up 8,000 companies in 24 hours". VentureBeat. Retrieved October 13, 2018.
  15. ^ Greenberg, Andy (March 27, 2015). "Slack Says It Was Hacked, Enables Two-Factor Authentication". Condé Nast. Retrieved October 13, 2018.
  16. ^ Sharwood, Simon (March 9, 2018). "Slack cuts ties to IRC and XMPP, cos they don't speak Emoji". Retrieved October 13, 2018.
  17. ^ Kim, Eugene (September 27, 2016). "Slack, the red hot $3.8 billion startup, has a hidden meaning behind its name". UK Business Insider. Retrieved October 13, 2018.
  18. ^ "Salesforce Signs Definitive Agreement to Acquire Slack". Retrieved January 21, 2021.
  19. ^ Lyons, Kim (January 4, 2021). "Slack starts 2021 with a massive outage". The Verge. Retrieved January 5, 2021.
  20. ^ "Slack kicks off 2021 with a global outage". AP NEWS. January 4, 2021. Retrieved January 4, 2021.
  21. ^ Johnson, Heather A. (January 2018). "Slack". Journal of the Medical Library Association. 106 (1): 148–151. doi:10.5195/jmla.2018.315. ISSN 1536-5050. PMC 5764588.
  22. ^ Crook, Jordan (July 9, 2015). "Slack Adds Emoji Reactions". Retrieved October 13, 2018.
  23. ^ a b c "Slack updated their privacy policy: Now your company can read 'private' messages". NBC News. Retrieved June 9, 2020.
  24. ^ Gebhart, Gennie (July 1, 2019). "Opinion | What if All Your Slack Chats Were Leaked?". The New York Times. ISSN 0362-4331. Retrieved June 9, 2020.
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  30. ^ Augustine, Ann (May 19, 2018). "A Review of the Slack Communication Service". Retrieved October 13, 2018.
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  33. ^ Coop, Alex (March 26, 2018). "Workday and Slack announce partnership; Google, Microsoft and Facebook on the horizon". IT Business. Retrieved October 13, 2018.
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  35. ^ a b Hotson, Dennis. "Building an Intelligent Bot Using the Slack API". Nordic APIs. Retrieved December 28, 2018.
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  38. ^ Novet, Jordan (April 20, 2015). "Slack brings its app to the Apple Watch (video)". VentureBeat. Retrieved October 13, 2018.
  39. ^ Bort, Julie (March 9, 2015). "5 Apple Watch apps that will help you do your job". Business Insider. Retrieved October 13, 2018.
  40. ^ Birnbaum, Ian (October 22, 2018). "You Can Now Receive Slack Messages Inside a Super Nintendo Game". Vice Media.
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  46. ^ Kumparak, Greg (July 26, 2018). "Atlassian's HipChat and Stride to be discontinued, with Slack buying up the IP". TechCrunch. Retrieved October 13, 2018.
  47. ^ Konrad, Alex (July 8, 2020). "Slack Acquires Corporate Directory Startup Rimeto, Plans To Operate It As Standalone App". Forbes. Retrieved July 9, 2020.
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  56. ^ "Form S-1 Registration Statement". Retrieved May 7, 2019.
  57. ^ "Slack: workplace message app so cute you want to use it at home". Financial Times. March 25, 2015. Retrieved October 13, 2018.(subscription required)
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  60. ^ a b Cohn, Cindy; Gebhart, Gennie (February 14, 2018). "The Revolution and Slack". Electronic Frontier Foundation. Retrieved October 13, 2018.
  61. ^ Reitman, Rainey (July 10, 2017). "Who Has Your Back? Government Data Requests 2017". Electronic Frontier Foundation. Retrieved October 13, 2018.
  62. ^ Silverman, Jacob (December 2016). "Big Bother Is Watching". The Baffler. No. 33. Retrieved December 11, 2018.
  63. ^ Finley, Klint (March 16, 2016). "Open sourcers race to build better versions of Slack". Wired. Retrieved October 13, 2018.
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  67. ^ "Slacks new policy lets bosses read employees dms without consent". March 22, 2018. Retrieved February 10, 2019.

External links[edit]