Microsoft should have been the most natural choice of in-team communication. While their sales team was busy selling crappy software to large companies and ignoring small ones someone built a kick-ass product called Slack.

It does not make sense for Microsoft to buy slack. Microsoft already has the sales muscle to reach millions. What Microsoft does not have is a product that can compete with Slack. They should build it ASAP as part of their Office suite. Skype is not that solution.