M4 is a powerful software tool for building knowledge systems and embedding intelligent processing in applications. Knowledge systems, also known as expert systems, are computer programs that embody knowledge or experience to make decisions and solve problems effectively. M.4 can be used to develop a variety of applications (e.g., selection, analysis, scheduling, configuration, diagnosis, planning, and design applications) in many diverse areas (e.g., manufacturing, finance and administration, field service, data processing and management information systems, sales and marketing, training, and education).