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.
Setalist - The easiest way to make awesome lists for the internet
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
Hunter TechLookup - Create lists of websites by technology for free
Better Uptime - We call you when your website goes down
Techmap.io - Techmap is a workplace search engine to find companies using technologies (e.g., Rails, PHP, Java, etc.) that are used internally. Finally, a "Google for Workplaces" that helps people find a place to work with technologies they love!