Slack, which has grown like wildfire among businesses large and small, was recently targeted as a potential acquisition target by Microsoft executives, but the deal was killed Microsoft co-founder Bill Gates and CEO Satya Nadella, according to a report at TechCrunch.

The debate was reportedly waged on rather predictable grounds: On the one hand, Microsoft has bought all the pieces needed to own this space, and is already in virtually every large business out there. On the other hand, Slack's obviously doing something right that Microsoft's many communication pieces haven't quite been able to duplicate.

Slack's chief executive, Stewart Butterfield, has been open about his ambitions to make Slack the way that companies manage their employee databases, challenging Active Directory by getting its messaging app into the hands of as many employees as possible, and then building a rich ecosystem around it.

Just this week, Slack added another piece to that ecosystem, rolling out voice calling in-app — and getting a little closer to Skype as Skype works to become a little more Slack-like.