Prototype design and testing is an indispensable stage of any project development in many fields of activity, such as aeronautical, spatial, automotive industries or architecture. Scientists and engineers rely on prototyping for a visual confirmation and validation of both their ideas and concepts. Using computers for designing digital prototypes is not a new idea since CAD applications are nowadays widely used. In this paper we present how new advances in 3D interaction and real time visualisation research domains lead to the development of a collaborative and really interactive system for virtual prototyping. This work is supported by the European Community through the ESPRIT programme 4.