Nmap or (Network Mapper) is a free open source tool that is used by many network administrators for security analysis created by insecure.org. Nmap can be used in may different ways, including checking a range of IP addresses to see what hosts are on the network. It can also be used as a post scanner to tell you which ports are open on a specific host computer. Nmap has been made to run on most popular operating systems such as Windows, MAC OS, and Linux.