NicOS is a simple x86 command line operating system that I am making for fun and to learn new things.
Building the source code can be done with a gcc cross compiler, the compiler toolchain can be built from source code found here, or a prebuilt compiler can be downloaded here.
To Build the source code on linux, just run make.
No idea you can figure it out yourself.
To run the OS I recommend using QEMU, simply run qemu-system-x86_64 -fda os-image.bin