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.
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
Oh Dear! - Website monitoring, without the hassle
Monkey Test It - Primate powered algorithms that scan your site for common bugs and SEO mistakes.
Freshworks - Delight your customers, from wherever you are
NIXStats - SaaS monitoring tool for window/linux servers and websites. Think up-time robot but with more features.