EpiSim is the tentative name for the spatial simulation engine written by Loren Cobb. Yes, he is well aware that other epidemic simulations already exist with that precise name.
EpiSim is a command-line edition of spatial epidemic simulation that Dr. Cobb has had under development since 2001. It uses population density data from Columbia University's Gridded Population of the World project.
The mathematical model employed in this simulation is Hoppenstaedt's discrete-time version of the reaction-diffusion equations of spatial epidemics.
The User Guide for the latest version of EpiSim can be found at this link: EpiSim User Guide.