Short for Network Mapper, an open source utility for exploring networks or doing a security audit. It is available without charge and was developed to quickly scan large networks. It performs well in this environment as well as with single hosts.
Nmap utilizes raw IP packets in novel ways to ascertain a number of things, including which hosts are available on the network, which services a host is offering (including application name and version), which operating system software and OS version is running, what type of packet filters/firewalls are being utilized, and more. Nmap runs on most types of computers (with console and graphical versions obtainable) and is obtainable with complete source code under the terms and conditions of the GNU GPL.
Insecure.org. Nmap. [Online, 2004.] Insecure.org Website. http://www .insecure.org/nmap/.