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
Seagull is a multi-protocol traffic generator. Especially targeted towards IMS, Seagull supports Diameter (RFC3588 and all applications) over TCP/SCTP and IPv4/IPv6 , TCAP (over SS7 or Sigtran), XCAP over HTTP and Radius.