Microsoft Mechanics Video: Microsoft Releases Teams Free version.

A great tool for small and medium-sized business communications, aiming at replacing #SLACK.

Ideal for business owners, this tool is free for up to 300 users, with worldwide support in 40 languages.

From the Microsoft Website, here are some of the features of this version:

Unlimited chat messages and search.
Built-in audio and video calling for individuals, groups, and full team meetups.
10 GB of team file storage plus an additional 2 GB per person for personal storage.
Integrated, real-time content creation with Office Online apps, including built-in Word, Excel, PowerPoint, and OneNote.
Unlimited app integrations with 140+ business apps to choose from—including Adobe, Evernote, and Trello.
Ability to communicate and collaborate with anyone inside or outside your organization, backed by Microsoft’s secure, global infrastructure.

The only requirements for the free tier are either a corporate or consumer email (outlook or gmail will work)

You can sign up at the Teams Site.