Serpstat - Search analytics, Rank tracking, Backlink analysis and Site Audit tool.
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.
Screpy - Screpy is a web analysis tool that can analyze all pages of your websites in one dashboard and monitor them with your team. It's powered by Lighthouse and it also includes some different analysis tools (SEO, SERP, W3C, Uptime, etc).
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
SEMRush - All-in-one Marketing Toolkit for digital marketing professionals.
Better Uptime - We call you when your website goes down