Startup Toolkit - Interactive how-to guides to launch your startup
BuiltWith - Find out the technology behind websites
Bites - Ready to use modals and popups
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
MakerMove - Discover great resources for makers and founders.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.