Enterprise Office 365 customers have had access to the Yammer network service for some time, and now Microsoft have made the same enterprise-based corporate network available to certain Office 365 Business packages (Premium & Essentials) and Office 365 Education customers.
Yammer is billed as a private social network, helping employees discuss and work together using tools similar to those they enjoy on open social networks, including a timeline for status updates, discussion groups and easy document sharing. With Office 365 integration, Yammer will provide SharePoint integration, a Yammer feed within the Office 365 portal and Office web app integration (though not all features are currently available).