Most apps built with Electron, and similar, run with HTML (you can argue that it's mostly JS, but it's all rendered in the HTML DOM).
Many STB's and modern TV's run some kind of HTML/browser engine. Some graphics engines for TV broadcasts. Plenty of kiosks and digital signage.
I thought about HTML as a format for note taking or as an alternative for PDF. Stuff like that.
You can certainly take notes with HTML but it seems people would rather use markdown. So far as "alternative to PDF" I'd say SVG is based on similar capabilities (vector graphics.)
For either one of those cases people might use "the web" to store or deliver those HTML files.
I don't really understand what you mean with the http and web stuff. I recently began downloading sites with the SingleFile Add-on for Firefox. I get a html file out of it. If I want to open it, I need something to render it. Which is my browser ,but could be something not web-related as well, couldn't it? Doesn't make it that a normal file format?
It is normal for an HTML file to point to resources outside the HTML file, that is, even if it is an HTML file on your hard drive it might point to images, Javascripts, etc. on other servers.
It certainly is possible to draw a circle around an HTML document and put the resources into a ZIP file, that is
https://en.wikipedia.org/wiki/EPUB
I bring up the analogy with "CD Rom" because physical media are kinda on the outs today. There was the time I had to get a 30GB file somewhere overnight by the end of a sprint (I got DSL) and the people were shocked that I sent a Blu-Ray. Tell people that a USB thumb drive is a competitor for cloud storage for sharing files with friends and co-workers and they are absolutely scandalized.