ncdu - A disk usage analyzer with an ncurses interface, aimed to be run on a remote server where you...
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.
Gdu - Gdu is one of the smart open-source disk analyzers specially designed for Linux that provides you complete information related to the disk space.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Baobab Disk Usage Analyzer - Baobab Disk Usage Analyzer is one of the light-weight disk analyzers that offers you a chance to view and monitor the disk usage & folder structure without any hassle.
Better Uptime - We call you when your website goes down