I'm using JRules 6.5.3. I am not loving it. It is really slow.
There is an eclipse-based IDE called ILog Rule Studio. It works somewhat, but builds are slow and you can't use the most recent jvm.
It is restricted to Java 1.4 and Java 5. If you use anything more current, some features of the ILog plug-ins won't work. Ruleset or RuleApp exports did not work until I installed the latest 1.5 JDK.
To use JRules you go through a process of "verbalization". You associate, hopefully, understandable English phases with java code. But doing a verbalization is painfully slow. When you verbalize, the save operation takes an amazing amount of time. I would say 10-30 seconds.