[anta40]

I still stick with xv6: https://github.com/mit-pdos/xv6-public

- It's not only a kernel, but also have user space

- Code is pretty compact and well documented, in general can be understood in a few days

- No need to spend hours to custom build gcc. Just use the one provided by the distro package manager

The x86 version isn't mantained anymore. They switched to RISC-V.

[notorandit]

I would give Minix3 a try.

[anta40]

No doubt it's more feature complete than xv6. Probably will try it on weekend.

[notorandit]

Don't forget to contact AST in case you get some interest.