I am also looking for this.

I envision an OS that handles networking, remote maintenance and updates and possibly even some scheduling for multiple applications, so that I don’t have to do all that in my application code. I don’t see what conceptually would make this hard and it would be a great step up in hobbyist development experience to me.

As far as I’m aware NuttX (POSIX-like) even has a shell, so I don’t see what should be so hard about it (please correct me).

Edit: Apparently Zephyr is also gaining support for this. Whoever builds a simple platform on top of one of these definitely had my attention.