nmap -- Network exploration tool and security scanner<hr>
<a href="http://www.insecure.org/nmap/">http://www.insecure.org/nmap/</a><hr>
Nmap is a utility for network exploration or security auditing.
It supports ping scanning (determine which hosts are up), many port
scanning techniques (determine what services the hosts are offering), and
TCP/IP fingerprinting (remote host operating system identification). Nmap
also offers flexible target and port specification, decoy scanning,
determination of TCP sequence predictability characteristics,
reverse-identd scanning, and more.
</listing>