Since you do not mention if you're already a pro with OS internals and implementations, I will assume, maybe incorrectly, that you're not. So in that spirit, try the XinuOS. It has the complete source code for a minimal, clean and practical OS. Search for the book explaining it inside out. xv6, a re-implementation of Dennis Ritchie's and Ken Thompson's Unix Version 6 (v6) also comes to mind. And C. Don't forget to sh…
> XinuOS Did you mean https://en.wikipedia.org/wiki/Xinuos or https://www.amazon.in/Operating-System-Design-Approach-Secon... ?
Yes, that's the book.
The source code is open-sourced,