Jess

"Jess [Java Expert System Shell] is a rule engine and scripting environment written entirely in Sun's JavaTM language by Ernest Friedman-Hill at Sandia National Laboratories in Livermore, CA.

Java/Jess/JessML (declarative xml rule language)
Java Virtual Machine
FAQ; documentation; mailing list; examples; third party plug ins and libraries; wiki ...

See also: Knowledge, Demon, Expert system, Inference, Knowledge base