Slack is a group messaging or team collaboration app that aims to simplify communication for businesses. Features include open discussions, private groups, and direct messaging, as well as deep contextual search and message archiving, and file sharing. Slack integrates with a number of other tools, such as MailChimp, Dropbox, and Google Drive.
The product is free to use, and also has paid plans with more features and greater controls.
The company has raised $340M in funding and boasts 800k users.