Yammer is a free, private microblogging service like Twitter, for making companies and organizations more productive through the exchange of answers to the question: "What are you working on?" It allows users to post updates of their activities, follow others' updates, tag content, and create memes.
As employees answer that question, a feed is created in one central location enabling co-workers to discuss ideas, post news, ask questions, and share links and other information. Yammer also serves as a company directory in which every employee has a profile and as a knowledge base where past conversations can be easily accessed and referenced.
Anyone in a company can start their Yammer network and begin inviting colleagues. The privacy of each network is ensured by limiting access to those with a valid company e-mail address. The basic Yammer service is free. Companies can pay to claim and administer their networks.