Threes is a puzzle game made by three people (Asher Vollmer, Greg Vohlvend, and Jimmy Hinson) in which you match numbers, continuously trying to save space on the playing board (the game ends when the board is full, and you have no more moves available) while trying to match large numbers for larger scores.
There's two things which Threes has slightly going against it, but once you start playing you realize that they're both unimportant. The first is the price factor. At $1.99 on the App Store, Threes isn't really denting anyone's income severely, however for some when a game isn't free to play then it isn't on their radar. The second is the fear which some people (including me) have of arithmetic/number games. While one might expect that achieving a high score in a game called Threes would require a mastery of mathematic abilities, success in this game is based upon understanding the systems in order to make the best move to free up space, combine numbers, and have the next number on the board be in a useful position.
Threes innovates in its design and game systems, making for a game which is immensely satisfying and adorable to play. Already Threes has stormed to the top of the App Store's paid applications, and it won't be long before just about everyone you know with an iPhone is playing it. Fortunately, now that I've finished writing this up, I can go back to playing Threes.