BuiltWith - Find out the technology behind websites
Email Marketing Academy from MailerLite - Learning platform for email marketing expert certification
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Brevo - Innovative online Email Marketing solution to manage your contacts, create & send your newsletters and track your results. More than 80 000 clients. Best prices and attractive features.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
Grade My Email - Helps you get out of the spam folder.