Team communication app Slack today said that it now has more than 4 million daily active users, up from more than 3 million in May.

And the service now has more than 1.25 million paying users. It had 930,000 paid seats in May.

Today Slack also said that Slack teams have installed 6 million apps (and that 6 millionth was task management app Trello). The free plan allows teams to have up to 10 free apps or service integrations.

Slack DAU

Above: Slack DAU

Image Credit: Slack

Slack’s growth since the app’s launch in February 2014 is a modern illustration of hockey-stick growth. Many third party software sellers, including Google, have made their tools compatible with the service, and cloud services like Salesforce-owned Quip have taken steps to incorporate Slack-like functionality.

“Continued momentum on the Slack platform is an important sign of the expanding role we play in the business software,” Slack said in a blog post.

San Francisco-based Slack now has 650 employees.