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).
I was excited about the Precursor when it was first announced, but over $500 for a bespoke password manager — albeit one with a ton of features and theoretically good security — was too much. It’s nice to see more info about the OS that runs on it.
Now I want to dig out my Palm PDA and set it up as a password manager, it will give me a reason to carry it on my belt at work like it’s 2001!