CogNos was supposed to be a mostly Smalltalk OS - as I understand it, the C and assembler code is just for booting and catching interrupts. The device drivers, file system, and network stack are all in Smalltalk. In addition to the repository, there is this conference paper:

https://charig.github.io/assets/papers/SCDE-DLS.pdf

The paper says "there would certainly be much more work needed before one could consider deploying our system." The project seems to be inactive now.