Website.informer: complete data lookup & free aggregated report on any domain including whois, visitors, IP & DNS details, competitors, owners, etc
WhoIsHostingThis identifies the web hosting provider for any domain, returning server location, nameserver data, and registrar information.
Whoisology is a cross-referenced database of current and historic domain ownership records for InfoSec, legal, and research professionals.
Whoxy provides a WHOIS lookup API with reverse WHOIS search and historical domain registration data for infrastructure investigation.
theHarvester collects emails, subdomains, IPs, and employee names from search engines and DNS records for passive OSINT reconnaissance.