Summary form only given. The ARGUS three-dimensional simulation code has been used for a wide variety of problems which require the solution of field equations and particle flows in complex geometries. Some of the applications include the determination of resonant modes in RF and accelerator structures, the electrical stability of MMIC (microwave monolithic integrated circuit) packaging, antenna design, gun design. the calculation of S-parameters for solid-state devices, and the calculation of RF component characteristics in the presence of dielectrics and magnetic materials. Combinatorial geometry is used in ARGUS to configure simulations for a wide class of problems. In applying ARGUS to the large problem set described above, it has been possible to verify the ability of large E-M simulation codes to produce accurate solutions, and to do so in a way that is useful for design