Discrete-event simulators are important scientific tools and the focus of a vast body of computer science research that is directed at their efficient design and execution. The JiST system, which stands for Java in Simulation Time, follows a long line of simulation frameworks, languages and systems. JiST is a new Java-based discrete-event simulation engine with a number of novel and unique design features. The purpose of this document is to expose those features with examples, to describe the overall functioning of the system and to leave the reader with an understanding of how to use JiST to construct efficient, robust and scalable simulations.