#1 Yammer

Purchased for: $1.2 billion

Date: June 25, 2012

Yammer, is a freemium enterprise social network service that was launched in 2008 and sold to Microsoft in 2012. It is used for private communication within organizations and is an example of enterprise social software. Microsoft was apparently looking for a social network element to add to its overflowing enterprise portfolio when it picked up Yammer. It came in as an addition to Microsoft's Dynamics, Sharepoint, and Office 365 suites and was meant to be a way to drive up adoption of other Microsoft services.

Though Yammer's user base has grown from 5 to 8 million and sales of paid networks, business model is still antithetical to that of Microsoft's core model, which is sell wide-reaching access to services and products through contracts.

Then Microsoft started selling Yammer for free and then tried to sell companies on other features. Ballmer praised freemium concept, saying "Yammer is a great adoption model and we want to pour more content into it." But it's unclear whether Ballmer's vision will come to fruition, especially given his early exit.

Verdict: Unclear.

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