"The Algernon rule-based inference system has been reimplemented in Java and interfaced with Protege. Algernon performs forward and backward rule-based processing of frame-based knowledge bases, and efficiently stores and retrieves information in ontologies and knowledge bases."
v3.4.0 was released on May 16, 2003.
With Jena 2 supporting pluggable inferencing I wonder how much effort it will take to get Algernon in there. There's a list of 14 things (not quite 100) you can do with Algernon (number 9: "Act as a server for remote rule processing"). The original was written in C++.