MenuetOS
www.menuetos.net
What Jamie wrote
An entire OS written in x86 assembly? 🤦🏼♂️ That sounds like a task you would give some CSci students in college to drive them slowly insane. You can boot it on a USB drive if you want to be an operating system tourist and take a peek. Notably this is one of those real-time operating systems that is likely behind the navigation system in your car.