Featuring elements of Scrabble mixed with a bit of Tetris, the mobile version of PopCap’s massively popular PC game is here to test your brain power. In order to accumulate big points, there’s a grid of randomly placed letters, from which you form words that are at least three letters long by tapping adjacent letters. The longer the word, the better—and not just because it generates higher scores. If you use too many short or common words, red tiles appear that burn their way through the playfield; if one of them hits the bottom of the game board, it’s game over. If you get stuck, you can shake the iPhone or iPod touch to redistribute the letters. We like this game’s smoothly escalating difficulty ramp, which provides a challenge without being overly harsh on newbies.