Owler - Owler is a crowdsourced data model allowing users to follow, track, and research companies.
BuiltWith - Find out the technology behind websites
Whatagraph - Whatagraph is the most visual multi-source marketing reporting platform. Built in collaboration with digital marketing agencies
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
QlikSense - A business discovery platform that delivers self-service business intelligence capabilities
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.