This paper proposes a novel approach -SART-to the development of real-time systems which is based on super actors,i.e.,actors whose behaviour is modeled by state charts.SART borrows structural concepts from known methods for reactive systems like ROOM and UML-RT,and favours as of construction by making actors reusable and composable software components. The distinguishing factors of SART are its modularisation of timing constraints and customisable scheduling algorithm. Application actors are not aware of timing requirements.RTsynchronizers capture timing constraints in groups of actors,filter relevant messages and control their scheduling.Time clauses of causally connected messages in system interactions ae directly derived from the declarative specification of end-to-end timing constraints.SART supports both prototyping and real-time execution modes. A SART graphical development environment supporting modelling,temporal property checking and code generation has been implemented in Java.