Have you ever had a problem that required managing a huge amount of rules? Written code to simplify giant nested conditionals? Then a rules engine, like Drools, might be for you!
If your problems have extended one step further, and you've needed to efficiently figure out the "best" type of schedule, distribution of employees, or other vague, high combination systems, then OptaPlanner might be a perfect supplement.
Come hear Kevin Greene talk about both!