StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Hyperping - Cheap uptime and performance monitoring with detailed reporting and flexible alerting
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.
Inline Checkout - Inline is a fully secure All-in-one Checkout, Upsells, Discounts, and Cart Recovery App for eCommerce - Shopify & WooCommerce
UptimeRobot - Free Website Uptime Monitoring
Checkout X - Checkout X is an all-in-one, checkout platform optimized to maximize conversion rates and revenue on WooCommerce stores.