You're technically right (the best kind?), but there's some nuance to the question.

FrameOS is a compiled binary that runs on top of Linux. At present you need to install the "Raspberry Pi OS Lite" (without the desktop environment) on a SD card before you can install FrameOS itself on top of that. So it's "just an application".

However, this is mostly because it's an early project, and this was the fastest way to get going. The next step is to see how much can be removed. Since FrameOS is a statically compiled single binary, it shouldn't need that much more than the Linux kernel? Will FrameOS be a true OS then? Android seems to be considered its own OS despite using the Linux kernel.

Once activated, FrameOS takes over your entire system, has its own `apps/` and `drivers/` folders, and in many ways already behaves like an Operating System. I'm also pondering about getting it running on an ESP32 (will need to add `drivers/wifi/`?). Without any OS below it, will it then be worthy of being called an OS? You all tell me. :shrug:

Thus is it an Operating System? It is to me, but you can choose to disagree.

At my actual job (PostHog), we sometimes call ourselves the "Product OS". This annoys me more, as a suite of webapps definitely isn't an "Operating System" in its traditional sense. I've seen -OS at the end of other things as well that aren't pure Operating Systems. It slightly bothers me, but mostly because I was around when "what OS you're using" was a defining question. Language is evolving, and "operating system" seems to describe more things to different people, than it does to you and me.

You're already aware of the word "kiosk," so why not market it explicitly as a kiosk?

It appears so, which would mean it could probably work with only minor changes on other boards.

Yeah it seems more like a full screen application which can be remotely controlled.

What is an OS? Genuine question, not being sarcastic here. "OS" is a pretty loosely defined term at the moment. Clearly Android and Ubuntu are very different operating systems, despite having roughly the same kernel.

FrameOs uses Nim, which means it can be ported to run on bare-metal with no kernel. The async dispatch means that Nim also provides some light-weight co-operative multitasking.

I'd say that FrameOs is an OS (or userpsace if you prefer) that currently only runs on top of the linux kernel, but there's no reason it couldn't be ported to run directly on a microcontroller.