Hunter - Find all the email addresses related to a domain
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Snov.io - More leads. More sales. More revenue.
BuiltWith - Find out the technology behind websites
Apollo.io - Apollo’s predictive prospecting, sales engagement, and actionable analytics help the teams to reach its full revenue potential.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.