As of tomorrow, PlayStation Plus subscribers will be able to download two games for free and save on another. Those are Metro: Last Light (PS3), Outlast (PS4), and Dustforce (PS Vita -- $7.99), respectively. That last title is also part of a larger PS Vita-specific sale, by the way.
If you have the means to do so, I'd recommend getting all three. I loved the setting and atmosphere of Metro 2033 but not its gunplay, so Last Light turned out okay for me; Outlast was undoubtedly one of last year's best horror titles thanks in large part to its focus on survival, not combat; and Dustforce is a well-put-together platformer with a marvelous soundtrack.
Later this month, subscribers will also get Payday 2, Remember Me, Street Fighter X Tekken (PS Vita), and ModNation Racers: Road Trip.
PlayStation Plus: Outlast and Metro: Last Light Free for Members [PlayStation Blog]