Global DNS allows you to instantly check DNS records on multiple servers. It provides end users with an idea of which server the website is pointing to.
Demo: https://codecanyon.net/item/global-dns-multiple-server-dns-lookup/25869388
WHOIS Lookup is a full featured PHP script that can search for WHOIS information on any website.
Demo: https://codecanyon.net/item/whois-lookup-ultimate-whois-information-checker-script/28782038
WhoisBooks is a Domain Whois Lookup PHP Script and Domain name-based registration information searching system.
Demo: https://codecanyon.net/item/whoisbooks-domain-whois-lookup-php-script/26823224