One of the ultimate plaintext champions is (unsurprisingly) John Gruber, the "inventor" of Markdown.

One of my favorite facts about his site, daringfireball.com: You can add the extension .text to any permalink and it will render that page as markdown:

- HTML: https://daringfireball.net/linked/2022/03/01/mozilla-on-tind...

- Markdown: https://daringfireball.net/linked/2022/03/01/mozilla-on-tind...