Slack—one of our 50 Smartest Companies for 2015 (see “The New Water Cooler”)—has grown rapidly since launching in February 2014, and on Wednesday the maker of work communication software offered some new insights about just how popular it’s gotten.

Slack says it now has over 1 million active users each day. That’s a big number for any company, especially one that is less than two years old, though to put it in some sort of perspective, it’s about 1/936th of the amount of daily active users Facebook sees (considering a stat on the social network’s website that cites its March traffic).

Slack makes a searchable, archivable instant-messaging app that connects to lots of other tools and services like Dropbox and Google Drive, letting users share files, alerts, and so forth in one place instead of spreading them out over a slew of apps and e-mail inboxes.

Slack also said that its users include 300,000 “paid seats,” which refers to the number of people using Slack as paying customers. So far, Slack said, it has more than $25 million in annual recurring revenue.

Slack also announced on Wednesday that it added April Underwood, formerly Twitter’s director of product for advertising and data, as its head of platform. She’ll be in charge of things like Slack’s platform products, partnerships, and relationships with developers.