Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.
BuiltWith - Find out the technology behind websites
My Codeless Website - My Codeless Website is a website scanner that detects themes, page builders, plugins and tracking tools. It's a super simple tool to get a quick summary of any website.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
Hunter - Find all the email addresses related to a domain