Choices helps you order your favorite things. You import a set of similar things, like a Music playlist from your Music app or a Moment from your Photos app. Choices then presents you with a choice between two of the items in the set, and asks you to pick the one that you prefer between the two. You repeat this choosing game over time. As you play, the app builds an ordered, weighted list of your preferences across the set of things, using a mathematically sound ELO rating system like the one that backs Nate Silver's work at fivethirtyeight.com
Choices is a powerful, flexible engine for ordering and grouping preferences in a mathematically sound way.
It is easy to expand the engine to support additional kinds of sets.
It would be easy to expand the engine to crowd-source preferences across groups of people: useful for social scientists or marketers alike.
The engine persists in Core Data currently and has been designed to easily accommodate other persistence mechanisms.