BuiltWith - Find out the technology behind websites
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.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
StatusCake - Website Uptime Monitoring & Alerts – Free Unlimited Downtime Monitoring
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
Better Uptime - We call you when your website goes down