Not a steam giveaway but.... Its free; 15hrs, 57min left.

http://www.gog.com/news/free_games_fallout_fallout_2_and_fallout_tactics

http://www.gog.com/promo/fallout_series_giveaway_winter_promo_2013

Noticed this, granted, cannot be redeemed on steam (I think, I honestly didnt check and am currently assuming it cannot be claimed on steam).

Codes are indefinite though and will not expire.