We describe a real-time software engineering toolkit called ASSERTS that provides complementary analysis and simulation capabilities to assist the designer of multiprocessor/distributed real-time systems. ASSERTS allows users to describe the parameters of the hardware platform, interconnection and the kernel, the programming model (shared or distributed memory) and the task system for the purpose of simulation and analysis. The simulation component of ASSERTS is quite detailed and features a number of built-in simulation models for practical real-time schedulers, interconnections as well as models of resource access protocols (such as priority inheritance and priority ceiling protocol). Users can describe the behavior of the tasks at various levels of abstraction using a fairly small set of about 20 macroinstructions for the purpose of simulation.