https://techcrunch.com/2019/04/09/slack-integration-with-office-365-one-more-step-toward-total-enterprise-integration/

Slack’s goal of integrating enterprise tools in the chat interface has been a major differentiator from the giant companies it’s competing with like Microsoft and Facebook. Last year, it bought Astro, specifically with the goal of integrating enterprise productivity tools inside Slack, and today it announced new integrations with Microsoft OneDrive and Outlook.

Specifically, Slack is integrating calendar, files and calls and bringing in integrations with other services including Box, Dropbox and Zoom.