Microsoft said that its daily active users have risen from 13 million to 20 million on its workplace app.
The software maker offers the app as part of some Office365 business packages, as well as a free version. Teams allow users to chat, share files, make calls and hold web video conferences.
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Microsoft Teams, used by companies such as General Electric and SAP,competes with Slack Technologies.
Slack, whose customers include Electronic Arts and Nordstrom, reported more than 10 million daily active users in the second quarter ended July 31.
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Slack’s shares fell 8.4% following the news, to $21.18. They are down 45% from the close of their first day of trade in June.
Microsoft Teams also competes with Workplace by Facebook and Cisco Systems’s Webex Teams.