Jetstream is a real-time stream processing system for analyzing live event streams to enable business to react to signals much earlier than is possible with batch oriented systems like Hadoop.

It is targeted for security, risk, machine learning, fault monitoring, predictive analytics and many more use cases where there is a need to track, detect and react to user or machine behavior patterns over windows of time. Examples of these could be monitoring DOS attacks, predicting failures by watching metrics, correlating events etc.

Follow wiki for more details.