I played with the Ultibo Operating System some time back, it is to much of a complete OS for bare metal work, at least in my personal view.
This is not an operating system! The OS is a program which allows to run another program by accessing its API via system calls. The Ultibo doesn't allow this. It is a programming environment only. You cannot write a program to run "on Ultibo": you can write a program with Ultibo, which runs itself without any OS, starts fast and allows you to use any hardware resources you want to.
Yes, it has a lot of things which normal OS has: a scheduler, threads, etc, but it still is not OS. Maybe someone will write an OS based on it (I only wrote an early alpha version of GUI)..
Though I would still like to figure out how to use HW decoding without having to dig through the Linux sources.
The Ultibo way to do this was to recompile "userland" C libraries to make them usable for Ultibo. (.a static linkable format, delete/replace Linux dependencies). Maybe they can be useful without the rest of the environment. Maybe not.