|Original author(s)||Stewart Butterfield, Eric Costello, Cal Henderson, and Serguei Mourachov|
|Initial release||August 2013|
|Operating system||Windows, macOS, Linux, iOS, Android, Windows Phone, Commodore 64|
Slack is a cloud-based set of proprietary team collaboration tools and services, founded by Stewart Butterfield. Slack began as an internal tool used by his company, Tiny Speck, in the development of Glitch, a now defunct online game. The name is an acronym for "Searchable Log of All Conversation and Knowledge".
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.
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. 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. Users can add emoji buttons to their messages, which other users can then click on to express their reactions to messages.
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. 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. 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. Major integrations include services such as Google Drive, Trello, Dropbox, Box, Heroku, IBM Bluemix, Crashlytics, GitHub, Runscope, Zendesk, and Zapier. In December 2015, Slack announced their app directory, consisting of over 150 integrations that users can install. 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.
Slack provides mobile apps for iOS, Android, and Windows Phone (beta), 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. It was featured on the home screen of the Apple Watch in a 2015 promotional video.
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.
The company originally raised nearly $43 million in April 2014. 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.
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. In April 2015, the company raised another $160 million. In April 2016, the company announced that it had raised an additional $200 million in funding.
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.
8,000 customers signed up for the service within 24 hours of its launch in August 2013. 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. 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.
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. 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".
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.
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