Courtesy of Bethesda, the following cosmetic items have been made free for a time, for the following titles:
DOOM Eternal (click for details)
Lux Slayer Special Edition Set , which includes the Lux Slayer skin, Lux Ballista Weapon skin, “Murder Magnate” nameplate, and “Fancy Pants” icon.
Majestic Archvile Special Edition Set , which includes the Majestic Archvile skin, “Your Highness” nameplate, and “Monarchvile” icon.
Nightmare Marauder Special Edition Set , which includes the Nightmare Marauder skin, “Night Terrors” nameplate, and “Sleep Paralysis” icon.
Wolfenstein: YoungBlood (click for details)
Legacy Pack , which includes the “New Colossus Jacket” and “BJ’s Army” Power Suit skins, the Old Blood Pipe & Knife weapons, and the WW2 Army weapon skin set.
Rage 2 (click for details)
Golden Weapon Bundle , which includes nine gold weapon skins, the Doombringer Bundle , which includes five weapon skins based on DOOM, and the Apocalypse Weapon Bundle , which includes four unique Assault Weapon skins.
Note, these are free in-game cosmetics, not free games.
You need to sign up to Bethseda’s newsletter via their official website to get the above items for free.