I am aware of two cross-platform audio libraries that cover OS X, Windows and Linux: RTAudio and PortAudio
I'm aware of a couple that support OS X and iOS: Novocaine and TAAE
However, I can't find anything that supports OS X, Windows and Linux and also iOS, Android
Does such a technology exist?
(https://www.juce.com/)(JUCE) was my choice in the end.
It is a C++ platform with a focus on real-time audio. I don't know how I missed it in the original question.
JUCE has gone from strength to strength over the past few years. Recently they have reorganised the licensing model so as to encourage independent/indie developers.
Don't want to sound too much like an advert, but I'm very happy with this technology stack.