Easy Rules is a Java rules engine inspired by an article called "Should I use a Rules Engine?" of Martin Fowler in which Martin says:

You can build a simple rules engine yourself. All you need is to create a bunch of objects with conditions and actions, store them in a collection, and run through them to evaluate the conditions and execute the actions.

This is exactly what Easy Rules does, it provides the Rule abstraction to create rules with conditions and actions, and the RulesEngine API that runs through a set of rules to evaluate conditions and execute actions.