Industry is facing a crisis in the design of complex hardware/software systems. Due to the increasing complexity, the gap between the generation of a product idea and the realisation of a working system is expanding rapidly. To manage complexity and to shorten design cycles, industry is forced to look at system-level languages towards specification and design. The (formal) system-level modelling language called POOSL is very expressive and is able to model dynamic hard real-time behaviour and to (visually) capture static (architecture and topology) structure in an object-oriented fashion. The language integrates a process part, based on the process algebra CCS, with a data part, based on the concepts of traditional object-oriented programming languages and it is equipped with a formal semantics. Currently, a number of automated software tools (model editing, simulator and compiler tools) are available in an environment called SHESim. These tools allow visual entry of structure and topology of the system, whereas dynamic behaviour of individual processes is expressed in an expressive imperative language. The formal semantics of POOSL provides a solid basis for the application of verification and performance analysis techniques and establishing a rigorous connection to existing analysis tools.