We are evaluating rules now for use with our application server. We have come across OpenRules, which is easy to integrate with Java and, as far as our testing has shown, fast enough. The main advantage of OpenRules above the others is the way the rules are modified and handled. It all happens in Excel tables, which is the easiest way for non-programmers. Everybody involved, even the non-technical people, understood everything perfectly :-)
We also have drools integrated, but the rules are way more complicated to understand as it is a more programmatic approach. That's why we - most likely - will stick to OpenRules.
