Cobalt Strike - Advanced threat tactics for penetration testers.

ViewDNS.info - Free DNS related tools including Reverse IP Lookup, DNS Propagation Checker, Chinese Firewall Test...

Shodan - Shodan is the world's first search engine for Internet-connected devices.

Whats My DNS - Instantly check your domain names current IP address and DNS record information against multiple name servers located in different parts of the world.

Censys - Censys helps organizations, individuals, and researchers find and monitor every server on the Internet to reduce exposure and improve security.

NsLookup.io - A simple and powerful tool for querying DNS records