JotaleaOS: a very tiny hobby operating system

JotaleaOS is an open source, minimalistic, experimental operating system made by Jotalea, designed for extreme low-resource environments. It does not support external programs or games, as it lacks a standard application execution environment. The system is entirely self-contained, running only its built-in commands.

JotaleaOS website

Exactly what is says on the tin: a tiny operating system created entirely as a learning experience. That's it.