Well, is any of this actual bare-metal environments for coding?
It's more of a HAL meets RTOS, and it's certainly not self-bootstrapping in Go, which is impossible on real hardware, or?
Astrobe is certainly bare metal, just like some of the Java deployment options, with AOT compilation to target boards, like Aicas and PTC are capable of.
If you want an example of GC in bare bones all the way from building your own FPGA up to the graphics display, check the 2013 update from Project Oberon.
implementing in a non-garbage collected lower-level language, of course.
Even FORTH's stack requires some ASM words to set it up...
or am I missing something here?
C, C++, Rust, possibly Ocaml, FORTH, FreePascal, etc... or else you are actually on about a virtual machine, not bare metal.
Learning how to create your own heap. Make your own malloc/free on a baremetal device and that will be a huge boost for you, confidence wise...