statuspage - A simple self-hosted status page site with an API written in Django under the BSD license.

BuiltWith - Find out the technology behind websites

StatusPage.io - StatusPage.io is the best way for web infrastructure, developer API, and SaaS companies to get set up with their very own status page in minutes. Integrate public metrics and allow your customers to subscribe to be updated automatically.

Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.

UptimeRobot - Free Website Uptime Monitoring

WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.