Nmap

Nmap is a free and open-source network scanning tool for inventory and security auditing. It helps determine which hosts are up, what services they offer (including version detection), what operating systems they run, and what network filters or firewalls may be present. It supports a variety of scan techniques and can be used for both large networks and single host assessments.

Created by Gordon Lyon (Fyodor) and released in 1997, Nmap runs on Linux, Windows, macOS, and others. It is maintained as an open-source project and released under the GNU GPLv2 license. The project includes the Nmap Scripting Engine (NSE) for extended detection and vulnerability checks.

Core features include host discovery, port scanning, service version detection, OS detection, and scripting. It supports TCP SYN, TCP connect, UDP, and IP protocol scans, as well as evasive and noisy options. It can perform aggressive timing controls and output results in multiple formats (normal, grepable, XML, and a 3-line summary with -oA). It also provides Zenmap, a cross-platform graphical user interface.

Use and considerations: Nmap is widely used by network administrators, security professionals, and researchers for inventory, vulnerability assessment, and compliance. Its use on networks without authorization may violate laws and policy. It should be used responsibly and in accordance with applicable rules, with explicit permission.