Aero is a new modern, experimental, UNIX-like operating system following the monolithic kernel design. Supporting modern PC features such as long mode, 5-level paging, and SMP (multicore), to name a few.
MollenOS/Vali is a modern operating system that is built with focus on abstraction and a modular design, allowing anyone to port it to any architecture. Supports i386, amd64 and aarch64