This is a syntax highlighter created for the language that you end up making in the Nand2Tetris course. It is a simple assembly langauge, and highlights keyword like JMP, JGT and it highlights variables and labels as well.
Install the package on your local Atom text editor by searching for language-hack-assembly, and it will recognize files under .asm, .hack, and .hck
Hope this helps that assembly programming slightly more :)