Since the late 1970s multistate structure functions have been introduced to overcome the shortcomings of the classical and binary approach to the structural aspects of systems and their components. The uncertainty about the state of a system and its components, classically is described by probability theory. Recently, several new models are proposed that are based upon fuzzy set theory and possibility theory. The spread and success of these models, however, highly depend upon the development of computer tools that allow the reliability engineer to apply these new methods rather easily. In this paper, we present such tool, CARA — Computer Assisted Reliability Analysis — which is able to represent and study the multistate aspects of systems and their components when only incomplete information is available.