Nmap (“Network Mapper”) is a free and open source utility for network exploration or security auditing. It was designed to rapidly scan large networks, but works fine against single hosts. Nmap uses raw IP packets in novel ways to determine 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. 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)
Source: https://thehackernews.com/2011/02/nmap-551-latest-version-out-now.html