CompeteShark - Real-time competitive intelligence software for SMBs
BuiltWith - Find out the technology behind websites
Accordably - Competitor monitoring made easy.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Apptopia - Apptopia provides app store downloads, revenue, and SDK data for every mobile app & every publisher in the world
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.