Yammer is an Enterprise Social Network that brings together people, conversations, content, and business data in a single location. With Yammer, you can easily stay connected to coworkers and information, collaborate with team members and make an impact at work. And because Yammer can be easily accessed through a web browser or mobile device, you can connect and collaborate with coworkers anytime, anywhere.
More than 200,000 companies worldwide use Yammer to engage employees, collaborate and innovate. As a platform, Yammer integrates easily with other systems to connect all of your business applications in a single social experience.
Founded in 2008, Yammer was acquired by Microsoft Corporation in 2012 and is now part of the Microsoft Office Division.
Cut back on meetings and email chains. Work together in a Yammer Group: a flexible, collaborative workspace for teams to get work done wherever, whenever. Discuss project deadlines, share the latest files, gather feedback – and more.
To enable Yammer for Office 365 Enterprise E series plans read these instructions: http://office.microsoft.com/en-us/office365-sharepoint-online-enterprise-help/pick-your-enterprise-social-network-yammer-or-newsfeed-HA104037368.aspx
Also please read this article: "Make Yammer your default social network in Office 365", at: http://blogs.office.com/b/office365tech/archive/2013/06/10/make-yammer-your-default-social-network-in-office-365.aspx
After you have setup Yammer as the default social network in Office 365 have your users enable their account by entering their Office 365 email address and creating their own Yammer password here: https://www.yammer.com/company/sharepoint
Try it today!