|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 team collaboration tools and services, founded by Stewart Butterfield. Slack began as an internal tool used by their 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 was 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, encrypted 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 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). 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. Major integrations include services such as Google Drive, Trello, Dropbox, Box, Heroku, IBM Bluemix, Crashlytics, GitHub, Runscope and Zendesk. In December 2015, Slack announced their app directory, consisting of over 150 integrations that users can install. 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 advertises itself as a freemium product available for an unlimited number of users, but it was reported by Quincy Larson 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.
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 include 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.
Slack provides mobile apps for iOS, Android, and Windows Phone (beta), in addition to their web browser client and native 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 promotional video.
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, those numbers had grown to 200,000 paid subscribers and a total of 750,000 daily active users. In 2015, Slack passed more than a million daily active users.
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".
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