The person who wrote this wrote it to be booted directly from BIOS. That means it must handle everything an OS would otherwise do for it: bootloader, resource management, hardware access, random number generation, etc. So a project like this has great value as an introduction to low level systems and OS development.
As someone who has written no-os code, you do not need to do everything the OS does. If you do not mind giving up most of your RAM, you can stick to realmode and take advantage of the BIOS functions (you can work around the RAM limitation by jumping between modes). If your computer has UEFI, you have access to a much more advanced set of functions, and (for many purposes) can target that. I haven't done anything beyond hello world type stuff on UEFI, but it feels like you can get alot done without noticing the lack of an OS.
UEFI is awesome in terms of what it enables you to do without an OS, but once you install a few tools like an EFI shell, it's at least as much of an OS as DOS ever was.
