BuiltWith - Find out the technology behind websites
Ghostery - Privacy tool for transparency and control
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Disconnect - Make the web faster, more private, and more secure. Disconnect lets you visualize and block the invisible sites that track your search and browsing history.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
Privacy Badger - Privacy Badger blocks spying ads and invisible trackers. How is Privacy Badger different from Disconnect, Adblock Plus, Ghostery, and other blocking extensions?