Bulk Whois API - Bulk Whois API is a provider of parsed WHOIS data in JSON with simple API, competitive pricing, top notch support, and more.

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.

Whoisology - Connected database of whois records and whois history

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.

WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.

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