You set up a free account in Prismatic and start to select topics that interest you. You like or dislike them, comment on stories -- something the above-mentioned news apps don't allow -- and you can discuss what you find with other Prismatic users or friends. You can also share on Twitter and Facebook.
The Prisimatic developers say they can find more unique and relevant things for you to look at, and I agree. The app isn't burdened with a lot of the noise that appears in Facebook and Twitter. Content choices are broader than some social apps, because it goes beyond friend recommendations. It scours the web for interesting material. In that way, it is like Zite or Flipboard, but the integration of direct social interaction can make for a more powerful experience.
Prismatic CEO Bradford Cross told me the back end of Prismatic analyzes millions of stories every day, and has indexes of more than 10,000 topics. I found it easy to find topics that aligned with my interests.
So far, the app is free, but it's likely ads will follow at some point, personalized alongside my interests. That's not a bad thing. With a lot of the special interest magazines I get, I'm as interested in the ads as the regular content.
I think Prismatic is a winner. I can judge it best by the content it finds, and it's doing a good job at that. I'm following a few people, and some are following me back. Video is not supported yet, but it's coming.
Privacy is always a concern with social apps, and Prismatic has published its policies here. Obviously, the more Prismatic knows about you, the better it can serve your needs, but there are options to remain anonymous.