Free SNMP simulator tools?

Try this one: http://snmpsim.sf.net

This is basically a SNMP Agent that reports back static values as taken from its backend (text files). You could either dump a snapshot of a real SNMP agent into a text file for snmpsim or create them from the scratch.

The tool is cross-platform and SNMP v3 capable.

You can also try www.gambitcomm.com, they provide SNMP Simulator for Single device version for Free.

I have recently written an SNMP v1 simulator in golang. I have written a simple programming language to specify OID variables and how they change. In one example, I used it to simulate a printer for page counts and error changes. Its aim is more about focusing on particular OIDs of interest than basing off an SNMP dump (which some other simulators do).

The project can be found here: https://github.com/scorptec68/snmprun

The docs are here: https://github.com/scorptec68/snmprun/wiki

The download is here: https://github.com/scorptec68/snmprun/releases