All APE executables are also unikernels that boot from BIOS. Here's a demo video of the APE executable for SectorLISP (ANSI C version) running in the Blink emulator (which I wrote originally just to test this): https://storage.googleapis.com/justine/sectorlisp2/sectorlis... When you compile an APE program with cosmocc, the first 512 bytes are a master boot record where we embed a BIOS bootloader in the PE DOS stub section of the executable. APE is then able to tell when the BIOS is what loaded it, switch to 32-bit mode, set up the page tables, enter 64-bit long mode, and then call _start() and main().

I personally haven't been focusing on bare metal support myself the past several months, but we've got a talented member of the team (tkchia) who actively works on maintaining metal and expanding its capabilities. See also the list of supported system calls for bare metal here: https://justine.lol/cosmopolitan/functions.html As you can see, we still have a lot of work to do. But it's really cool to have, and I have high hopes for it someday as a cloud native deployment format. Hypervisors are in many ways the new OSes, so why do we need a traditional OS in-between?