There are 2 repositories under hobby-kernel topic.
A book that explore how to write an Operating System from scratch
opuntiaOS - an operating system targeting x86, ARM and RISC-V.
An x86 monolithic kernel and operating system written in modern C++. Comes with in-house graphical applications and command line utilities, plus ports of existing software. And yes, it runs DOOM!
A hobby operating system written in Zig & C, a modification of some UNIX ideas.
An OS based on UEFI
Almost usable x86-64 Unix-like kernel
Tiny Kernel is a work in progress Operating System kernel.
Kernel for my operating system KoraOS
An AArch64 hobbyist OS for the Raspberry Pi 3 B+
floppaOS is a free and open source 32 bit operating system made in C. It is themed around the famous internet Caracal "Big Floppa"
Learning operating system and kernel development by building a multithreaded OS called ToyOS
SkylightOS is a small, portable and extensible RTOS
A basic x86 kernel to learn how operating systems get from BIOS to userland
World's simplest operating system from scratch
An x86 32-bit operating system
Me Operating System is a Unix-like c/c++ operating system targeting the intel x86 architecture.
A Simple Operation System + Kernel I Write In My Free Time
An OS based on the OSDev bare bones C kernel and Meaty Skeleton. Help wanted and appreciated!