DNSChecker.org - Check DNS Propagation worldwide. DNS Checker provides name server propagation check instantly. Changed nameservers so do a DNS lookup and check if DNS and nameservers have propagated.

Cobalt Strike - Advanced threat tactics for penetration testers.

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.

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

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

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