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 / 2 months ago
DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
DNSdumpster.com - Open source domain intelligence lookups for security recon
WebCargo - Optimize your workflow by offloading it to us. Useful API's with seamless integration that scale to your needs.
WhoisAPI - WhoisAPI is the premier provider of freshly parsed whois data for domain names and IP addresses...
Flagfox - Flagfox is a Firefox extension that displays a flag depicting the location of the current websites...
CyberIntel.Report - CyberTOOLBELT is a comprehensive set of tools designed to make the investigation of domains, IP addresses and other related information efficiently and effectively.