Out of Your Head by Darrin Fong.
Impulsifier by jaakopassan.
https://github.com/jaakkopasanen/Impulcifer. Not the only piece of software needed. Head Fi has fuller explanation of what's needed and how it all fits together.
Redscape has some hardware (a head tracking unit), but is pretty cheap and I've heard it works fairly well.
Or you could just cough up the $3995 plus freight and duty, and get yourself a Smyth A16 Realiser, the gold standard for this kind of thing.