Honeyd is a small daemon that creates virtual hosts on a network.  The
hosts can be configured to run arbitrary services, and their personality
can be adapted so that they appear to be running certain operating
systems.  Honeyd enables a single host to claim multiple addresses on a
LAN for network simulation.

It is possible to ping the virtual machines, or to traceroute them.  Any
type of service on the virtual machine can be simulated according to a
simple configuration file.  Instead of simulating a service, it is also
possible to proxy it to another machine.