|Original author(s)||Stewart Butterfield, Eric Costello, Cal Henderson, and Serguei Mourachov|
|Initial release||August 2013|
|Operating system||Microsoft Windows, macOS, Linux, iOS, Android, Windows Phone|
|Available in||8 languages|
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.
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.
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.
Slack offers many IRC-style features, including persistent chat rooms (channels) organized by topic, private groups, and direct messaging. 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.
Slack's free plan allows only the 10,000 most recent messages to be viewed and searched.
On March 18, 2020, Slack redesigned its platform to simplify and customize the user experience.
Slack teams allow communities, groups, or teams to join a "workspace" via a specific URL or invitation sent by a team admin or owner. Although Slack was developed for professional and organizational communication, it has been adopted as a community platform, replacing message boards or social media groups.
Private channels allow for private conversation between smaller sub-groups. These private channels can be used to organize large teams.
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.
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 and Zapier. In December 2015, Slack launched their software application ("app") directory, consisting of over 150 integrations that users can install.
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.
Slack provides an application programming interface (API) for users to create applications and automate processes, such as sending automatic notifications based on human input, sending alerts on specified conditions, and automatically creating internal support tickets. Slack's API has been noted for its compatibility with many types of applications, frameworks, and services.
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), and Linux (beta). Slack is also available for the Apple Watch, allowing users to send direct messages, see mentions, and make simple replies. It was featured on the home screen of the Apple Watch in a 2015 promotional video. Slack has been made to run on a Super Nintendo Entertainment System via Satellaview.
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)". That specific limit no longer applied by January 2017.
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.
8,000 customers signed up for the service within 24 hours of its launch in August 2013. 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. By April 2015, those numbers had grown to 200,000 paid subscribers and a total of 750,000 daily active users. Late in 2015, Slack passed more than a million daily active users. As of May 2018[update], Slack had over 8 million daily users, 3 million of whom had paid accounts. 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.
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. In 2017, New York magazine criticized the platform for being "another utility we both rely on and resent."
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". 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, 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.
Slack has been criticized by users for storing user data exclusively on cloud servers under Slack control. 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".
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