It competes with Slack, a very popular app for enterprise (and other) collaboration.
Microsoft Teams is included in some of Office 365 subscriptions and is well integrated.
Architecture of Teams is a bit unusual for Microsoft product:
it is based on client side web technologies, including Angular and related,
and is packaged with "web shell" based on Electron/Chromium.
Essentially Microsoft is leveraging some Google's open source tools for new flagship product!
very informative interview:
The latest in Teams - MS Dev Show Podcast
Microsoft Teams PWA (Progressive Web App) Preview, but for Windows 10 S Mode only? - Tom Talks
"Microsoft Teams is built from the ground up using modern web technologies; Angular, TypeScript, Webpack, SASS and more. It uses over 200 different OSS components and is designed to share as much code as possible between different clients."