Microsoft Yammer, a service of Office 365, is a social networking service used for communication within organizations.
A collaboration solution that includes enterprise social, email, real-time collaboration, and file sync and share.
Users can post messages and respond to colleagues' messages, users can see messages from the people, groups and tags that they follow.
Social Collaboration: Groups, external collaboration, search, inbox and notifications, discovery feed, MS Office integration.
Desctop application, iPhone App, Blackberry App, Android App,Windows Mobile App, Text Message integration, eMail integration, Twitter integration, IM integration, MS Outlook integration, Microsoft sharepoint integration.