Network footprinting and reconnaissance
https://pentest-tools.com/blog/index.php/network-fingerprinting-using-online-tools/
https://pentest-tools.com/reconnaissance/find-subdomains-of-domain
http://www.nerdtools.co.uk/
https://pentest-tools.com/reconnaissance/find-subdomains-of-domain
http://www.nerdtools.co.uk/