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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.
Screenshot Machine - Screenshot machine is an online website capturing service. Creates a screenshot or thumbnail of any online web page in couple of seconds for free.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Urlbox.io - Screenshot full page websites in retina resolution with Urlbox.io screenshot as a service API. Urlbox is the best provider of automated website screenshots offering many unique options and features.
Better Uptime - We call you when your website goes down