TacOS: an x86_64 UNIX-like OS from scratch

TacOS is a UNIX-like kernel which is able to run DOOM, among various other smaller userspace programs. It has things like a VFS, scheduler, TempFS, devices, context switching, virtual memory management, physical page frame allocation, and a port of Doom. It runs both on real hardware (tested on my laptop) and in the Qemu emulator.
↫ TacOS GitHub page

TacOS – great name – is written in C, and explicitly a hobby and toy project. The code’s licensed under the Mozilla Public License 2.0.