Whois extractor is described as 'Extract email addresses of the domain owners. Get support of all types of domains, extra data gathering. Get a free trial now!' and is an app. There are four alternatives to Whois extractor for Online / Web-based and Self-Hosted solutions. The best alternative is DomainTools, which is free. Other great apps like Whois extractor are CubDomain, zonefiles.io and Domains Index.