Following up on December's offer of a free copy Borderlands 2 for PlayStation Plus subscribers, Sony is upping the ante for January. Starting January 2014, PS+ members on PlayStation 3 can download a free copy of BioShock Infinite, DmC: Devil May Cry, and Brothers: A Tale of Two Sons.
PS+ is Sony's subscription service that provides several member benefits including access to a rotating "instant game collection." The game's are only available to active PS+ members, and they are generally only available to download for free for a limited time (though once you've added them to your account, you can redownload the game again at any time).
PS+ is mandatory for online play in PlayStation 4 games. The service typically sells for $18 for three months or $50 for one year.