Fallout, Fallout 2 and Fallout Tactics are free from the Epic Games Store.
The old-school isometric role-playing games are collectively available now for free until 4pm UK time tomorrow as part of Epic's Christmas giveaway promotion. The trio replace yesterday's giveaway, Lego Builder's Journey.
At 4pm tomorrow, the Fallouts will themselves be replaced by another game, officially unannounced but rumoured to be tactical sci-fi RPG Encased.
Interplay's Fallout 1, 2 and Tactics are classics of their genre, and predate Bethesda's take on the series which kicked off with Fallout 3 and the move to first-person.
I can't recommend the first three Fallouts enough, so if for some reason they're not already knocking about on your Steam library, it's well worth nabbing them from Epic now.