Elevens is a solitaire card game in which players lay down cards, face-up and in a grid of 3X3. They then remove the cards in groups when they add up to eleven, and go until they can go no more.
Cassandra’s 11 is based on this game, in that you must tap cards from a grid when they add up to eleven. Tap a Nine and Two card, for example, or a Five, a Four, and a Two. What takes this universal app from developer Plexonic to the next level is the puzzle aspect.