Pragma - The home base for Ethereum developers.
BuiltWith - Find out the technology behind websites
Blockbutler - Real-time transaction notifications for the blockchain
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Pusher Beams - Send push notifications programmatically at scale
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.