Check the full post for details and an FAQ; also see the Teams press release and Announcing the Microsoft Teams Developer Preview (Office Dev Center)
"Today, at an event in New York City, we announced Microsoft Teams—the new chat-based workspace in Office 365. Microsoft Teams is an entirely new experience that brings together people, conversations and content—along with the tools that teams need—so they can easily collaborate to achieve more. It’s naturally integrated with the familiar Office applications and is built from the ground up on the Office 365 global, secure cloud. Starting today, Microsoft Teams is available in preview in 181 countries and in 18 languages to commercial customers with Office 365 Enterprise or Business plans, with general availability expected in the first quarter of 2017.Introducing Microsoft Teams—the chat-based workspace in Office 365 - Office Blogs
At Microsoft, we are deeply committed to the mission of helping people and organizations achieve more—and reinventing productivity for the cloud and mobile world is core to our ambition. We built Microsoft Teams because we see both tremendous opportunity and tremendous change in how people and teams get work done. Teams are now more agile and organizational structures more flat to keep communications and information flowing. With Microsoft Teams, we aspire to create a more open, digital environment that makes work visible, integrated and accessible—across the team—so everyone can stay in the know."