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.

BuiltWith - Find out the technology behind websites

DNSChecker.org - Check DNS Propagation worldwide. DNS Checker provides name server propagation check instantly. Changed nameservers so do a DNS lookup and check if DNS and nameservers have propagated.

Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.

NsLookup.io - A simple and powerful tool for querying DNS records

What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.