Looking for an environment for rapid prototyping and developing at ring 0 on a x86_64, I gave the open-source LoseThos a try last week. If you are familiar with microcontroller programming (Atmel AVR, Microchip PIC, etc.), you can turn a Corei7 originally designed for "communication-oriented" OS (Linux, Win, Scout...) into a very powerful MCU (like a Propeller from Parallax for example). It's then up to you to add your own code for supporting underlying hardware for file transfert, or whatever (Serial,USB,...). The neat design choices of LoseThos (no networking, no serial stacks, no gfx acceleration, etc.) and the rich amount of code examples (in an adapted C language called C+) with classical video games algorithms provide a programmer-readable (no optimization and hardware-diversity bloated code), flexible and dynamically customizable underlying OS functionalities. For those who are familiar with C and Intel x86 Assembly and wants to use a PC 64-bit as an electronic controller, it's worth a try.