Stack stands out with slick usability and a clever learning algorithm which updates your preferences with each swipe of the finger. The swipe-right to save/swipe-left to delete gesture is an addictively simple way of sifting through the news and a smart way for the app to learn about what it is you like reading. Interestingly, you can discover what other like-minded users are reading by choosing to follow them. This social feature means Stack offers the serendipity that most other aggregators lack.