Nikto is a highly regarded open-source (GPL) web server scanner that provides comprehensive testing for a wide range of web server components. It features the ability to identify over 6,700 potentially hazardous files and programs, check for outdated versions on over 1,250 servers, and perform version-specific scans on over 270 servers. Additionally, Nikto assesses server configurations, such as the presence of multiple index files and HTTP server options, and can determine the type of web server and software installed.