WebGazer - Monitor your website's availability with WebGazer, review its performance and get instant notifications when your website goes down. No installation required and free plan available.
Site Down - Site down outage and downtime reports from SiteDown.co
Oh Dear! - Website monitoring, without the hassle
Is it Down? - Is it down can check if a website is down or is it just your PC that can not access it.
Freshworks - Delight your customers, from wherever you are
UPDOWNtoday - UPDOWNTODAY allows you to check whether the website is down or not.