Nmap is a network utility for network inventory and security audit. Nmap checks host availability, host services, operating systems details, etc. Nmap has both GUI and CLI.
Nmap can be used on many operating systems like Windows, Linux, FreeBSD, OpenBSD, Solaris, IRIX, Mac OS etc.
There are some additional parts coming with Nmap.These are:
Zenmap : Result Viewer GUI
Ncat : Responsible for data transfer, redirection and debugging
Ndiff : Scan resuls compariment tool
Nping : Responsible for Packet generation and response analyse
You can download Nmap, below.