The structure and use of a message-passing multiprocessor simulator are described. The simulator provides a multitasking environment for the development of algorithms for parallel processors using either shared or local memories. The simulator may be used from C or FORTRAN and provides a library of subroutines for task control and message passing. The simulator produces a trace file that can be used for debugging, performance analysis, or graphical display. 9 refs., 7 figs.