Vero Newsletters - The first "baseless" email marketing tool.
BuiltWith - Find out the technology behind websites
Google Sheets Email Marketing - Email automation and validations directly from Google Sheets
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Opens Are Dead - Everything email marketers need to get ready for iOS 15
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.