SendView - The best way to track your competitors' email marketing.
BuiltWith - Find out the technology behind websites
Panguin Tool by Barracuda Digital - See your website's Google organic visit data overlaid with Google's major algorithm updates and changes to easily identify the impact on your website. Technology by Barracuda Digital.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Seolyzer - Seolyzer is the ultimate SEO tool that provides you with all the information you need to improve your website’s health and performance.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.