Many independent simulation tools address particular modelling aspects well, such as Neuron and Genesis for compartmental models, MCell for Monte-Carlo diffusion, and various neural network simulators. However, these tools don't interact with one another, so models built with one tool are not accessible to the others. Modellers often resort to writing their own simulations from scratch, when it is possible they could take advantage of some facilities in Neuron or Genesis.
Thus the Neosim kernel will provide mechanisms for coordinating a number of plug-in simulation and visualisation modules.