Popify App - Boost your conversions using social proof popups
BuiltWith - Find out the technology behind websites
WP Social Proof - Social proof for WordPress Websites
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
SocialProofed - SocialProofed is the easy way to embed Instagram feeds, Facebook reviews, and Google testimonials on your website...in just 60 seconds!
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.