BuiltWith - Find out the technology behind websites
AwesomeDigest - An email newsletter for every "awesome" list on GitHub 😻
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
DevScreen - Automated, practical interview assessments for developers
WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.
git:logs - The definitive list of open source resources on Github