BuiltWith - Find out the technology behind websites

Crunchbase - Crunchbase is a platform for discovering industry trends, investments, and news about companies around the world.

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

CB Insights - CB Insights is a company database for the venture capital and corporate development community.

WhatRuns - Extension that helps you identify technologies used on any website at the click of a button.

Tracxn - data on companies