The Netwide Assembler on a Mac
The Netwide Assembler or NASM, is an x86 and x64 assembler designed for UNIX operation systems. The assembler comes with documentation which will help you with the basics. It supports a multiple range of object file formats, including Mac, UNIX, and Windows formats.
It will also output plain binary files, Motorola and Intel formats. Its syntax is designed to be simple and easy to read and understand. The Assembler supports all existing x86 and x64 extensions, and has strong support for macos.