This package consists of three main components. The NESSUS (network definition language of the University of Stuttgart) compiler allows the generation of medium-sized to large structured nets using a programming language developed especially for this task. The output from the compile (an ASCII file) is read in by the kernel which builds its own data structures in memory. The graphical user interface, XGU, built on top of the kernel, gives a graphical representation of the neural networks and controls the kernel during the simulation run.