In this paper, we add predictable and resource efficient event-triggered tasks in an RTOS. This is done by introducing an execution model suitable for example control software and component-based software. The execution model, denoted single-shot execution (SSX), can be realized with very simple and resource efficient run-time mechanisms and is highly predictable, hence suitable for use in resource constrained real-time systems. In an evaluation, we show that significant memory reductions can be obtained by using the SSX model.