SaaS Email Marketing Handbook - Double Your MRR With Email Marketing
BuiltWith - Find out the technology behind websites
Elevatr Email Marketing Automation - Fast and easy email marketing software
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
HubSpot Free Email Marketing - Powerful drag and drop email marketing in the HubSpot CRM
WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.