Broadcasts a who-has ARP packet on the network and prints answers. VERY useful when you are trying to pick an unused IP for a net that you don't yet have routing to. (from the arping site)
Get it from http://www.habets.pp.se/synscan/programs.php?prog=arping
Never get "duplicate IP address found" messages on windows boxes anymore ... go unnoticed in an unknown network :-)
enjoy,
Dieter