Slack is currently valued at $2 Billion, and adding $1 Million in ARR every 12 days. These huge numbers can directly be attributed to the stickiness of the project and the depth of functionality that surrounds the chat application.
Though Slack officially launched just over a year ago, the app has seen truly remarkable growth in that time. At launch, in February of 2014, Slack had around 15,000 daily users.  By August of 2014, Slack’s daily active users had grown to 171,000, and that number had swelled to 285,000 by November.  By February of 2015, the app boasted over 500,000 daily active users, with “tens of thousands” of new users added week over week, representing a thirty-threefold growth in just a year. Not only that, but Slack users are collectively sending 300 million messages every month, and users are actively engaged with the app for more than two hours every day.