R9 is a work-in-progress effort to build a Plan 9 kernel to Rust. It was started a couple years back by the maintainers of the Harvey OS distribution of Plan 9, who threw in the towel after “loss of traction”.
R9 is a reimplementation of the plan9 kernel in Rust. It is not only inspired by but in many ways derived from the original Plan 9 source code.
↫ R9OS GitHub page
For now, the project is obviously mostly focused on running in virtual machines, specifically Qemu, in which it can be run using a variety of architectures: aarch64, x86-64 (with or without kvm), and RISC-V.