WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
HostedScan.com - Online vulnerability scanner for servers, networks, and web applications.
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.
HackerTarget.com - Security Vulnerability Scanning based on Open Source Tools.
Whoisology - Connected database of whois records and whois history
Intruder - Intruder is a security monitoring platform for internet-facing systems.