This may be interesting:
[Collapse OS] is a z80 kernel and a collection of programs, tools and documentation that allows you to assemble an OS that can:
- Run on minimal and improvised machines.
- Interface through improvised means (serial, keyboard, display).
- Edit text files.
- Compile assembler source files for a wide range of MCUs and CPUs.
- Read and write from a wide range of storage devices.
- Replicate itself.
Additionally, the goal of this project is to be as self-contained as possible. With a copy of this project, a capable and creative person should be able to manage to build and install Collapse OS without external resources (i.e. internet) on a machine of her design, built from scavenged parts with low-tech tools.
HN discussion: https://news.ycombinator.com/item?id=21182628