Clearbit Connect - Clearbit Connect is a free extension that surfaces actionable information on the people who email you.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Datanyze - The sales prospecting tool powered by technology data
BuiltWith - Find out the technology behind websites
DiscoverOrg - DiscoverOrg is an IT sales intelligence platform providing technology marketers access to data, IT org charts, and real time projects.
WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.