Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting

SEMRush - All-in-one Marketing Toolkit for digital marketing professionals.

Uptime Monitor by HetrixTools - Minimize your downtime by being the first to know about it

Website Checker Tech - WebsiteChecker.Tech is SaaS tool that detects SEO and availability issues of your website, making it easier for you to fix them.

Inline Checkout - Inline is a fully secure All-in-one Checkout, Upsells, Discounts, and Cart Recovery App for eCommerce - Shopify & WooCommerce

Moz - Backed by industry-leading data and the largest community of SEOs on the planet, Moz builds tools that make inbound marketing easy.