WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
Whoisology - Connected database of whois records and whois history
JSON WHOIS API - Parsed domain WHOIS data from any WHOIS server via RESTful API with metered pay as you pricing.
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...
WhoAPI - WhoAPI is an API service for mass requests of domain information like domain registration availability and structured whois data in JSON.