While not currently free, the Epic Games Store regularly gives away high-profile titles for free every week. It is worth monitoring their "Free Games" section for future rotations. Avoiding Pirated Versions
Frequently on sale for under $10 during seasonal events. state-of-decay-pc-game-free-download-full-version
Offers the "Play Anywhere" feature, meaning if you buy it on PC, you also own it on Xbox consoles. While not currently free, the Epic Games Store