[7][8] Slack originated as an internal communication tool used within Stewart Butterfield's company Tiny Speck, during its work on the development of Glitch, an online video game.

[9] These communication tools were initially built around the Internet Relay Chat (IRC) protocol and included scripts designed to automate and organize file exchanges among its development team.

In 2012, Butterfield decided to name their upcoming product "Slack", which he said was derived from the phrase "Searchable Log of All Conversation and Knowledge", replacing the previous codename "linefeed".

[17] In July 2020, Slack acquired Rimeto, a startup specializing in employee directories and profiles, with plans to rename the service and operate it as a standalone app.

[25][26] In August 2024, Box and Slack announced an expanded partnership that introduced secure AI capabilities to enterprise content management.

[27][28] In March 2015, Slack announced that it had been hacked for 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.

[35] Slack offers many IRC-style features, including persistent chat rooms known as channels, which are organized by topic, as well as private groups and direct-messaging functionalities.

[49][50] This integration allows employees to access co-worker information, organizational charts, benefits, feedback, and time-off requests within Slack.

In March 2023, Salesforce announced the partnership with OpenAI to launch a ChatGPT integration for Slack and can be used for summarizing conversations, answering questions, or drafting replies.

[58] Slack is a freemium product whose main paid features are the ability to search more than 90 days' archived messages and add unlimited apps and integrations.

[12][62] 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.

[68] 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.

[73] 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.

[79] Slack has also been criticized for a retroactive 2018 change to its 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.