BuiltWith - Find out the technology behind websites
CALCONIC_ - Build & add interactive calculators to your website! Choose from more than 50 premade calculators or build your own from scratch. No coding required. Free plan available. Zapier Integration. Publish Anywhere.
Wappalyzer - Wappalyzer is a technology profilers and leads data provider. Create lists of websites and contacts that use certain technologies.
ConvertCalculator - Create powerful, beautiful Calculator forms
What CMS - WhatCMS.org looks at a variety of factors within a webpage to determine what CMS a website is using.
Calcapp - Build apps instead of spreadsheets