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.
Airtable - Airtable works like a spreadsheet but gives you the power of a database to organize anything. Sign up for free.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
StatusGator - Monitor all your hosted applications, vendors, and websites, and keep your team informed of outages. StatusGator is the world's premier status aggregator, status page, and website monitoring tool.
Better Uptime - We call you when your website goes down
WrapAPI - Build an API on top of any website