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. 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.
Update Yammer Takes Top Prize At TechCrunch50 (USD50K) – Congrats 
Features needed to take off in a bigco are..