WhoisThisDomain - Domain name lookup tool that allows you to get information about domain registration from WHOIS server.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
WebCargo - Optimize your workflow by offloading it to us. Useful API's with seamless integration that scale to your needs.
BuiltWith - Find out the technology behind websites
Bulk Whois API - Bulk Whois API is a provider of parsed WHOIS data in JSON with simple API, competitive pricing, top notch support, and more.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.