Popcorn

Popcorn is a learning kernel: a small operating-system core you can boot in an emulator, read line by line, and change without fighting a huge codebase. When it starts, it prepares memory, a system clock, and basic multitasking, then opens a simple text console where you type commands—while a background clock keeps ticking so the kernel can switch between tasks.

If you already know OS terms, see the operation map for boot flow and interrupts, or the source catalog for every core/ and pops/ file and how they link.