Suprvise - Know instantly when your sites are down.
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.
PingPing - A simple tool to monitor your website and SSL
Oh Dear! - Website monitoring, without the hassle
Monitoro - Monitor webpages and get fresh data sent to your webhooks.
Freshworks - Delight your customers, from wherever you are