JEFF is a free, open source expert system explanation facility written in Java. It enables expert system creators to provide the HOW and STRATEGY explanations regarding the inference process. Since it is a Java framework, it is supposed to be a generic solution for modern rule-based systems. It is simple to use and can generate explanations in the form of natural language like sentences. Internationalization is also supported and explanations can be saved as textual, XML, RTF or PDF reports.
GitHub repository: https://github.com/bojantomic/jeff