Some of these games are normally offered for free, a few are "free" with a PS or Xbox subscription, yet some of these are truly free but can only be claimed as such for a limited time (however you get to keep them if you claim them in time). A few highlights include Samurai Shodown NEOGEO Collection, Ark: Survival Evolved, and Jill of the Jungle: The Complete Trilogy.
Here's the source and the listing of more free games (which are updated weekly at GameSpot):
https://www.gamespot.com/articles/fr.../1100-6474874/