Salesforce Chatter aims to transform the way you collaborate with people in your company. As both a collaboration application and a platform for building social cloud-computing apps, Chatter helps you connect and share information securely like never before - all in real time.
Yammer is a tool for making companies and organizations more productive through the exchange of short frequent answers to one simple question: “What are you working on?” 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