PlayStation Now is a pretty cool idea. 100's of PS3 games that you can stream to play over your PS4. While it is not true backwards compatibility it is pretty close, and if you never actually owned the games you could just play them from here. Downside is that it was super expensive comparatively to actually play the games. But that will soon no longer be a problem. Starting on 01/13/2015 you can subscribe to the service for $19.99 one month at a time or 3 months for $44.99 ($15.00 / month) for unlimited play of the entire catalog.
Also as a special bonus new subscribers (which should be just about everyone) will get 7 days free. Lastly if you download the free PlayStation Now theme on to your PS4 before the 01/31/2015 you will be entered into a drawing for one year subscription. Fingers crossed for them that this works out better then OnLive's first attempt at stream to play gaming.