This paper presents a Rapid Controller Prototyping System based on Matlab, Simulink and the Real-Time-Workshop toolbox. Executable code is automatically generated for Linux RTAI, a hard real-time extension of the Linux Operating System. The generated code runs as a normal user space hard real-time application on a standard personal computer with the RTAI extension of the Linux Operating System. This environment can be used to quickly implement real-time controllers. Moreover, standard hardware allows the use of rapid prototyping techniques not only during development activities but also during system operation. A didactic and an industrial application are presented which demonstrate the capabilities and the performance of the environment.