Don't get fooled by the free-to-play clones out there, Threes is the puzzle (math?) game that got the craze started, and it's the one you want to play, and that will keep you playing long after you get the hang of how it's played. It's almost too simple in principle: slide tiles on a 16-square grid to combine matching numbers that are multiples of 3 and see how high a number you can generate.
A flick of the finger moves the tiles in one of the four directions and brings an additional tile onto the board. Twos and ones can be combined into threes, which can be combined with other threes to make sixes. Sixes beget 12, which begets 24, which beget 48, then 96, and so on.
The developers imbued these numbers with personalities of a sort, and when you create one you'll find that they make sounds as you move them about the grid. That a puzzle game like Threes is voice acted is an indication of the level of detail and care that went into the game's creation.
The biggest number I've been able to generate in the hundreds of games I've played over the past few weeks is 192. But I keep playing, keep starting a new board of tiles in an attempt to go further.
Platform: iOS
Developer: Sirvo LLC