If you have a soft spot for a Z80 computer but want a new operating system experience, try Zeal. You can watch a demo of the open-source OS in the video below.
As you might expect, the whole system is written in Z80 assembly language. The features you expect are there: files, directories, device drivers, a clock, and even memory banking to support up to 16M of memory. The work isn’t totally done, nor is the initial target computer — Zeal — but it looks like a great piece of work so far and will be of interest to anyone who has a Z80.
You can also try it in emulation mode in your browser if you don’t have a Z80 CPU handy. The author wanted a simple OS that wasn’t multithreaded and could live in ROM. The kernel takes about 6K of ROM and 1K of RAM, depending on the configuration. The system calls and general operation will remind you of Linux.
There is a large list of things to do, so if you have a mind to pitch in, there’s no shortage of ideas to work on. Does the world need another Z80 OS? For that matter, does the world need any more Z80 systems? We don’t know about the world, but we can always use them. They don’t even have to cost very much.