Xous is a microkernel operating system designed for medium embedded systems with clear separation of processes. Nearly everything is implemented in userspace, where message passing forms the basic communications primitive.
↫ Xous website
It’s written in Rust, and it’s been around for a while – so much so it’s sponsored by NLnet and the EU. The Xous Book provides a ton more details and information, with a strong focus on the kernel. You can run Xous in hosted mode on Linux, Windows, or macOS, inside the Renode emulator, or on the one supported hardware device, the Precursor. Obviously, the code’s open and on GitHub (which they should really be moving to a European solution now that the Americans are threatening the EU with war over Greenland).
