seL4, the verified microkernel, jas been ported to RISC-V!
miniblog.
Related Posts
Looking back on 10 years of the verified seL4 microkernel: https://microkerneldude.wordpress.com/2019/08/06/10-years-sel4-still-the-best-still-getting-better/
Includes some interesting design notes and comments on avoiding a kernel heap entirely.
An interesting paper looking at bugs in the Linux kernel and exploring which wouldn't work on seL4: https://ts.data61.csiro.au/publications/csiro_full_text/Biggs_LH_18.pdf
(Also, apparently Google's Fuschia is based on the Zircon microkernel!)
The goals of Redox: https://www.redox-os.org/book/book/introduction/what_is_redox.html (Unixish and Linux compatible, but a microkernel with userland utilities all in Rust!)