Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
ViewDNS.info - Free DNS related tools including Reverse IP Lookup, DNS Propagation Checker, Chinese Firewall Test...
BuiltWith - Find out the technology behind websites
Whats My DNS - Instantly check your domain names current IP address and DNS record information against multiple name servers located in different parts of the world.
WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.
NsLookup.io - A simple and powerful tool for querying DNS records