Several open source operating systems are written in Rust. Most of them are only proofs of concept, or suitable as demos in courses on operating systems. The only system that goes a step further is redox (see https://www.redox-os.org), which is actively being developed. It has a microkernel architecture and comes with a window manager, as well as basic applications such as an editor and file manager. You can find a comparison of several Rust OS projects, as well as a great number of useful links on this site https://github.com/flosse/rust-os-comparison.
tock (https://www.tockos.org) is an embedded operating system written in Rust and designed for running multiple concurrent, mutually distrustful applications on low-memory and low-power microcontrollers.
cortex_m_rtfm is a bare metal concurrency framework for Cortex-M microcontrollers geared towards...
