What is nmap tool

Nmap tool

Nmap is an open source program released under the GNU General Public License
(see www.gnu.org/copyleft/gpl.html). It is an evaluable tool for network
administrators which can be used to discover, monitor, and troubleshoot TCP/IP
systems. Nmap is a free cross-platform network scanning utility created by Gordon
“Fyodor” Lyon and is actively developed by a community of volunteers.
A typical Nmap scan
Nmap’s award-winning suite of network scanning utilities has been in constant
development since 1997 and continually improves with each new release. Version
5.00 of Nmap (released in July of 2009) adds many new features and enhancements
including:
 Improved service and operating system version detection (see page 89)
 Improved support for Windows and Mac OS X
 Improved Nmap Scripting Engine (NSE) for performing complex scanning

Download from here
https://www.nmap.org