"Final Stand", a downloadable expansion pack for Battlefield 4, is currently On The House. This means it's free on Origin. But since it is a DLC, one must own the base game (Battlefield 4) in order to access it. Although if you don't have the base game, you can still just grab the DLC and keep it till you buy BF4.
Click here to grab the game.
You'll need to login to your EA account to add the game to your Origin library. Once added, it'll be yours to keep forever. But you'll require the Origin client in order to play the game.
If you don't have the client, get it here.
P.S. At the time of writing, Medal of Honor: Pacific Assault is still available to claim for free. But it may not be for much longer.