Not an OS, but Mozilla is rapidly updating pieces of Firefox with Rust (with lots of ideas & code coming from Servo). And while browsers don't necessarily match

Not an OS, but Mozilla is rapidly updating pieces of Firefox with Rust (with lots of ideas & code coming from Servo). And while browsers don't necessarily match the complexity of modern operating systems, I think that having Rust be part of something as complex as a browser will be good for Rust and systems programming. The project is called Quantum: https://wiki.mozilla.org/Quantum https://wiki.mozilla.org/Quantum