Yammer is a private social network that helps employees collaborate across departments, locations and business apps. As a collaboration software solution, it was purchased by Microsoft in 2012 for a cool $1.2 billion. Yammer allows you to quickly bring a team together for conversation and collaboration in one place, including data from different business applications.
Price is clearly a winning feature for Yammer. Its enterprise-level solution only costs a few dollars per user. Of course, if you have thousands of employees, that figure ratchets up pretty quickly, but then such companies also have the resources to make it happen.