DomainTools - Domain name research, including comprehensive Whois Lookup, Reverse Whois Lookup and Whois History.
Pingdom - With website monitoring from Pingdom you will be the first to know when your website is down. No installation required. 30-day free trial.
WhoisAPI - WhoisAPI is the premier provider of freshly parsed whois data for domain names and IP addresses...
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
JsonWhois.io - JsonWhois is the leading cloud hosted Whois API.
Better Uptime - We call you when your website goes down