I am currently learning assembler using NASM via books by Duntemann and others from Apress.
My long term ambition is to build a high-performance, high-precision, error-free library for numerical computing and then build applications using the same under macOS using it's AppKit UI library via the Metal interface.
I don't want to have the burden of downloading the entire XCode environment when all I need is an assembler and linker which I can ask a friend to build an installable package of.