Wikipedia
DTRules
DTRules is an Open Sourced Rules Engine written entirely in Java. DTRules executes Decision tables directly, and utilizes a Domain-specific language for expressing the conditions and actions within the Decision Tables.
DTRules is a Deterministic Rules Engine, meaning that the execution of the rules within the Decision Tables is ordered by the tables themselves. DTRules is not a production rule system, and does not currently use any implementation of the Rete algorithm.