NodeOS
Lightweight operating system using Node.js as userspace
... platform, but the general structure is barebones custom Linux kernel with an initramfs that boots to a Node.js REPL, initramfs Initram environment to mount the users partition & boot the system, and usersfs multi-user environment with the same behaviour of traditional OSes. All the layers are bootable, leading barebones to a raw naked Node.js REPL prompt as PID 1, while initramfs exec actual NodeOS code to isolate user code from the core system.