Short-reach transmission technologies based on multimode sources and fiber infrastructure remain highly attractive and competitive against single-mode solutions. We present here details of a versatile integrated multimode simulation framework targeting the design, analysis, and optimization of such systems. Important aspects that are addressed here are detailed multimode signal representations, mode solvers, models for signal propagation in multimode fibers, multimode VCSEL models, models to calculate the coupling between various multimode devices, and system-level building blocks specifying and measuring the characteristics of the overall system. The multimode VCSEL model, for instance, simulates different emission frequencies of the individual modes, considers their dependence on the bias current and laser temperature, and accounts properly for mode competition. In addition to accurate modeling of signal propagation in multimode fibers, statistical analysis of the link performance can be conducted to account for profile defects altering the fiber and link characteristics. A dedicated coupler model simulates launch conditions of multimode transmitters and assesses power coupling losses at fiber-fiber interfaces with the coupled devices being separated in free space and misaligned relative to each other. Besides discussing device modeling details, we present virtual test benches for measuring typical characteristics, such as the Encircled Flux of the launch system, DMD and EMBc of the multimode fibers, as well as system performance characteristics, to determine whether the simulated system and its individual components meet industry-accepted requirements.