https://great-coder.github.io/os/index.html
It's recommanded to compile this in Ubuntu 16.04 LTS
To compile the source code, you need to install
a c/c++ cross compiler (or you can use Ubuntu 16.04 LTS which has cross compiler),
nasm (Netwide assembler)
and qemu (or a VM).
After installing the prerequesties, in the main directory in terminal, type make vos. (You can type make help to get info and help)
After completing compiling, you can run generated .bin file with qemu or you can use .iso file to run it on any VM you want.