Siftery - Share products your company uses and get personalized recommendations
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Stackshare - StackShare is a comprehensive website that gives its users the chance to organize and share their technology stack with the rest of the community.
BuiltWith - Find out the technology behind websites
Software Product Management Stack - Resources & tools to help you manage your software product
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.