So, what exactly is a Yammer? Well, it’s a simple social network designed not to connect you with family or college roommates, but with with your coworkers. The platform has had some success, but its most high profile moment may be today’s announcement that Microsoft had purchased the company. Rumors had been circulating for about a week, but now Redmond has made it official and issued a press release announcing its plan to purchase the startup for $1.2 billion in cash. Yammer will continue to live on as a stand alone service, which should make its 5 million users and countless Fortune 500 customers happy. But Microsoft will certainly be looking to fold its features into its own suite of enterprise offerings, likeSharePoint and Office 365. For more info check out the PR after the break.