Within each team, users can create different channels to organize their communications by topic. Each channel can include a couple of users or scale to thousands of users.
Microsoft Teams works on Android, iOS, Mac and Windows systems and devices. It also works in Chrome, Firefox, Internet Explorer 11 and Microsoft Edge web browsers.
The guest-access feature in Microsoft Teams allows users to invite people outside their organizations to join internal channels for messaging, meetings and file sharing. This capability helps to facilitate business-to-business project management.
Teams integrates with Azure DevOps.
Note: Slack would also be a correct answer, but it is not an option here.