Rational Rhapsody is a software modeling and development tool that allows engineers and developers to design and test software systems, particularly in real-time and embedded systems. It provides features for visual modeling, simulation, code generation, and documentation. Users typically work with UML diagrams to represent various aspects of a system, such as actors, use cases, classes, and sequences. Rational Rhapsody is often used in industries such as aerospace, automotive, healthcare, and defense.