BuiltWith - Find out the technology behind websites
Site Rank Data - View historical rank information of websites via time series charts.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Q-Stats - Get free marketing insights for every question on Quora.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
HypeStat - HypeStat is free statistics and analytics service, where you can find information about every website.