"Nmap ("Network Mapper") is a free and open source (license)
utility for network exploration or security auditing. Many systems
and network administrators also find it useful for tasks such as
network inventory, managing service upgrade schedules, and
monitoring host or service uptime. Nmap uses raw IP packets in
novel ways to determine what hosts are available on the network,
what services (application name and version) those hosts are
offering, what operating systems (and OS versions) they are
running, what type of packet filters/firewalls are in use, and
dozens of other characteristics. It was designed to rapidly scan
large networks, but works fine against single hosts. Nmap runs on
all major computer operating systems, and official binary packages
are available for Linux, Windows, and Mac OS X. In addition to the
classic command-line Nmap executable, the Nmap suite includes an
advanced GUI and results viewer (Zenmap), a flexible data transfer,
redirection, and debugging tool (Ncat), and a utility for comparing
scan results (Ndiff).
"Nmap was named “Security Product of the Year” by
Linux Journal, Info World, LinuxQuestions.Org, and Codetalker
Digest. It was even featured in eight movies, including The Matrix
Reloaded, Die Hard 4, and The Bourne Ultimatum.
"As free software, we don't have any sort of advertising budget.
So please spread the word that Nmap 5.00 is now available!"