Nmap (Network Mapper) is an open-source network scanner that identifies open ports, running services, and operating system versions on target systems. It is one of the foundational tools in information security, used by defenders and attackers alike. The Nmap Scripting Engine (NSE) adds vulnerability scanning and service interrogation capabilities. In your ISMS, you can use Nmap for internal network audits to discover unexpected open ports or unknown services. Be aware that running Nmap scans without authorization from the network owner can raise legal issues.