Simon Harris has written a nice little JRules overview.
I have found it interesting to observe rules engines and where they fit in, with the average Java development. From my observations, there is one group that doesn’t leave home without them. A lot of logic goes through the business rule processes. The larger the enterprise projects, the higher the chance that you see these folks.
However, the majority of users developing web-based/GUI apps seem to ignore the world of the rules engines. Why is that? Isn’t there a need for these folks to have an engine do the heavy lifting?
I think that the two worlds are going to mix even more in the future… especially with the standard rules engine API, good open source solutions such as drools, and solid commercial products like ILog JRules.