CLIPS is a productive development and delivery expert system tool which provides a complete environment for the construction of rule and/or object based expert systems. Created in 1985, CLIPS is now widely used throughout the government, industry, and academia. The name is an acronym for "C Language Integrated Production System."
CLIPS is probably the most widely used expert system tool because it is fast, efficient and free. Although it is now in the public domain, it is still updated and supported by the original author, Gary Riley. CLIPS incorporates a complete object-oriented language COOL for writing expert systems. Though it is written in C, its interface more closely resembles that of the programming language LISP. Extensions can be written in C, and CLIPS can be called from C.