ViewDNS offers a nice, online collection of DNS and OSINT tools. The tools are also offered as an API to give webmasters the ability to easily integrate them into their own sites. A free API "sandbox" account has a monthly limit of 250 queries. Our appreciation for the recommendation goes to CingularIT. - Source: Reddit / about 1 month ago
JsonWhois.io - JsonWhois is the leading cloud hosted Whois API.
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
DNSdumpster.com - Open source domain intelligence lookups for security recon
EZwhois - Whois domain information such as registrar, domain status, expiration date, and name servers.
Domaintally - Domain name intelligence and analytics platform that provides comprehensive insight and key metrics...
WebCargo - Optimize your workflow by offloading it to us. Useful API's with seamless integration that scale to your needs.