plugtree

Drools first started as a RETE implementation in Java to take business rules and make it easier for developers and end users to define, modify and deploy ever-changing business logic. With time it evolved into a Business Logic Integrated Platform where not only rules are first class citizens but processes and events too.

Drools 5 support flows whom in concert with business rules makes a very expressive and natural definition of business processes.

The latest addition is Complex Event Processing (CEP), it handles large volumes of events and by using temporal operators you can infer, detect and act on temporal and/or sequential behavior such as fraud detection, intelligent automated trading, etc.

If you haven't tried to yet, you're missing much!!

Try out this messaging engine: it has a AIO enabled journal (only on linux using JNI)! This project is the continuation of jboss messaging 2.
I feel this is the killer open source JMS server