HubSpot Free Email Marketing - Powerful drag and drop email marketing in the HubSpot CRM
BuiltWith - Find out the technology behind websites
Email Marketing: A Beginner's Guide - Master email marketing with these 3 short ebooks from Drip.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Elevatr Email Marketing Automation - Fast and easy email marketing software
WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.