ModbusPal is a project to develop a PC-based Modbus simulator. Its goal is to reproduce a realistic environment, with many slaves and animated register values. Almost everything in ModbusPal can be customized and controlled by scripts.
SNMP Simulator is a software that would act like a multitude of real physical devices from SNMP Manager's point of view. Simulator builds and uses a database of physical devices' SNMP footprints to respond like their real counterparts do.
Project moved to GitHub: https://github.com/etingof/snmpsim