The math is simple. Graillon 2 and MAutoPitch are so good that many professional producers use them because the free options are lighter on CPU and have unique features (like Graillon's throat modeling).
Many websites promise a "Free Download" or a "Cracked Version" of Waves Tune i--- Waves Tune Real-time Free
, a professional-grade pitch correction plugin by Waves Audio. While the plugin itself is a paid product, here is a write-up on what it does, how it works, and the context regarding "free" access. What is Waves Tune Real-Time? The math is simple