Onix
YiYiYa
Dennix is a unix-like hobbyist operating system written from scratch
A UNIX-style Operating System for the Waikato RISC Architecture
An operating system inspired by brutalist design
A multi-threaded-style OS for the Spectrum +3
Learning operating system development using Linux kernel and Raspberry
An operating system written in C
A microkernel-based hackable operating system
Simplest kernel for cooperative multithreading
Haiway Edge Computing OS
Real time preemptive embedded multi-thread kernel
Ubuntu-based Linux Gaming OS
AquilaOS: UNIX-like Operating System
PRTOS is a simple, compact preemptive RTOS for embedded systems
A UNIX-like kernel for the i386 architecture
Mulithreading Arduno library
FreeMiNT is a free alternative OS kernel for Atari systems & clones
The extensible bootloader for embedded system
Chromium OS Universal Chroot Environment (EOL)
A Hobby OS in C and ASM.
What you see, is what you get! GNU/Linux Arch Based Distro
Embedded Real-Time Operating System (RTOS)