The recent advent of cyber-physical systems (CPSs) in end-user applications extends the need for sophisticated model creation, simulation and system verification to new application areas. CPSs such as smart homes seamlessly integrate technology into every-day life, rendering their safety and correctness paramount. The intricacy of these systems' modelling stems from the merging of two opposing views: While flows of physical energy are mostly described using mathematical methods such as differential equations, engineered applications are usually best expressed using discrete formalisms. This thesis describes the creation of the Continuous REactive SysTems language (CREST), a domain-specific language (DSL) dedicated to the combined modelling of physical resource flows and engineered behaviour. The language coherently merges architectural concerns, reactive dataflow and non-determinism. Its Python implementation allows convenient system modelling and supports advanced concerns such as the simulation and formal verification of hybrid systems based on sound theoretical foundations.