[monocasa]

It's absolutely tiny for one. It has less code than sel4, despite also including a userland and being a monlithic kernel.

It's essientially a stripped down rewrite of what existed in Lion's Commentary on Unix. When you reduce subsystems to around 1KLOC each, it's a lot easier to see the core of what they're trying accomplish.

As for what's missing... a lot. No threads, no mmap (or any way to share memory between processes), only vga, serial, lbs, and ide drivers (in the x86 port), no block devices in the fs, 20 something syscalls total.