Zenmap is a free and open source graphical network mapping and security auditing tool. It is the official graphical user interface for the Nmap Security Scanner, a powerful network exploration and security auditing tool used by network administrators and security professionals worldwide. Zenmap allows users to scan networks for devices, services, and security vulnerabilities, and provides an easy-to-use interface for configuring Nmap scans and interpreting the results. It can be used to quickly discover hosts and services on a network, map out networks and their components, and detect security vulnerabilities. Zenmap can be used to generate detailed reports on a network, including a list of live hosts, the services they are running, and any potential security issues. It can also be used to create custom Nmap scripts, which can be used to automate security audits.
Skipfish is no longer maintained. The latest version, 2.10 beta, released in December 2012, is still available for download from Google Code Archive