CEP or Complex Event Processing offers a great value proposition if your domain requires event based processing. And I believe a whole lot of scenarios require that. Do read about Espers offering here.

An excerpt from Esper web site:

Complex Event Processing, or CEP, is technology to process events and discover complex patterns among multiple streams of event data. ESP stands for Event Stream Processing and deals with the task of processing multiple streams of event data with the goal of identifying the meaningful events within those streams, and deriving meaningful information from them.

The Esper engine has been developed to address the requirements of applications that analyze and react to events. Some typical examples of applications are:

Business process management and automation (process monitoring, BAM, reporting exceptions, operational intelligence)
Finance (algorithmic trading, fraud detection, risk management)
Network and application monitoring (intrusion detection, SLA monitoring)
Sensor network applications (RFID reading, scheduling and control of frabrication lines, air traffic)

The best part is that Esper is available .Net and Java libraries both.