BuiltWith - Find out the technology behind websites
Telnyx SMS API - Build global text messaging right in your app
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
Pragma - The home base for Ethereum developers.
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
Slack RTM API - Slack's Real Time Messaging API