Xous, the OS that runs on the precursor, may be of interest to look at too:
https://github.com/betrusted-io/xous-core
It is written in Rust and is targeted for a RISC-V
https://github.com/betrusted-io/xous-core
It is written in Rust and is targeted for a RISC-V
Xous for devices.
There is also Hubris and TockOS for embedded and IT.
There are a few others.