Light weight old school web apps?

I wandered around to this website and was immediately impressed by its simplicity and elegance. So naturally I went to BuiltWith to see the magic behind it. But I didn't find much. It's a simple static website without any CMS behind it.

Looking at the code behind it I found some interesting light weight libraries that I'd never heard of, but they all were inspired by simplicity. Going down the rabbit whole further, I discovered the following, cool, lightweight libraries that I hope I will get time to play around with:

• https://prismjs.com/
• https://umbrellajs.com/
• https://picnicss.com/
• https://flickity.metafizzy.co/
• https://github.com/turbolinks/turbolinks

This website also reminded me of the retool.com