I think this thread is still mostly games that are temporarily free, although a few other freebies have snuck in. I think the early access games going from free to paid count since they're now temporarily free until the paid price kicks in. Also, notices of paid game that just went "permanently" free I think count here, especially since a "permanently" free game may disappear and no longer be distributed. I'm thinking of how Blizzard put Lost Vikings and a few of their older games up for free a long time ago on their site, and those links are now gone.
New, permanently free games are a much grayer area; they're not a perfect fit for this thread, but I don't know of a thread that's a better fit. If they're too much of a distraction, I guess a completely separate thread could be started.