To be pedantic for a moment...

> You can't use Go to write a kernel ...

Not a production kernel, but MIT did use Go to "study the performance trade-offs of using a high-level language with garbage collection to implement a kernel" [1]

There is also gVisor [2] which implements, as best as I can describe, a kernel in user space. It's intent is to intercept syscalls made in containers and to redirect its execution in a sandbox.

> ... program a microcontroller ...

I'm not sure if one would classify this as a microcontroller, but USB Armory did write a, iirc, Go compliant runtime for bare metal ARM and RISC-V [3].

There is also TinyGo [4] with the following listed microcontroller support [5]

[1] https://github.com/mit-pdos/biscuit

[2] https://gvisor.dev/

[3] https://github.com/usbarmory/tamago

[4] https://tinygo.org/

[5] https://tinygo.org/docs/reference/microcontrollers/