Microsoft Teams - a new chat-based productivity tool which allows users to collaborate in rooms with integrations to Office 365. It's very similiar to Slack if you've used that, but because it's Microsoft it has all the integrations to other Microsoft tools. You can have real time discussions, share files, and review a history of previous discussions. Hate tracking down emails or getting tons of 'reply all' emails? Teams is a great solution for that.
We featured Teams in a webinar a few months ago, and wanted to being it back again due the growing use and popularity If you have Office 365, you may even already have it.