Unexpectedly wasn't asked: How it compares to Redox, another message passing microkernel system written in Rust? Also, what for embedded devices means? What specific features has that other microkernel systems don't, or just means is limited in scope*?
*Contrast to Redox that is meant to be general purpose but also offers an embedded-oriented minimal version.
Can't comment on Redox as I'm not familiar with it (maybe xobs is), but "for embedded devices" means design choices are made to accommodate smaller memory footprints - hundred k's of RAM, ROM; not the gigabytes expected in desktop-class OSes. So, this is in the same class as e.g. zephyr, threadx, chibi-os, Tock, etc. and has no explicit aspirations to be able to run e.g. server workloads. An example of such a trade-off is sticking with a 32-bit pointer size from the get-go. No desktop or server-class OS could make that trade-off, but the memory savings from smaller pointer and object sizes is meaningful on a memory-constrained device.
*Contrast to Redox that is meant to be general purpose but also offers an embedded-oriented minimal version.