Alarm Pinger (apinger) is a little tool which monitors various IP
devices by simple ICMP echo requests. Unlike most Perl or shell
script tools, it does not spawn processes or use much CPU time,
and is ideal for when one wants continuous monitoring and fast
response upon target failure. It is written in C and supports both
IPv4 and IPv6.

WWW: http://www.bnet.pl/~jajcus/apinger/