ARTISST (ARTISST is a Real-Time System Simulation Tool) is a modular event-driven simulation framework for real-time systems. It is targeted towards the performance evaluation of complex dynamic real-time systems made of tasks performing arbitrary computations and exhibiting a complex and realistic pattern for their arrival law, synchronization relations, and execution time. The simulator actually focuses on a time-accurate simulation, since it allows, among other things, to take the operating system (including its scheduler) costs into account. Furthermore, thanks to its modular and object-oriented software architecture, the simulator is not dedicated to a particular Operating System API, but is fully customizable instead. This paper describes ARTISST, and illustrates its functionalities and customization facilities on two example real-time systems.