Available on the iPhone, "Arithmetics Free" is one of the few games geared specifically to adults, rather than simply having crossover appeal. The basis of the game is that it provides you with a number. Using the rules of mathematics (including addition), you must create that target number by choosing the correct three numbers on the screen. A timer requires you to think quickly to score points. Players can challenge other Arithmetics Free users to beat their score.
If you're looking for a game specifically created to boost addition skills, as opposed to arithmetic skills in general, "add k Mad" may interest you. Sheppard Software designed this program to help both children and adults learn addition. As in "Arithmetics Free," the game gives you a particular number. You must then create this number by choosing from a grid of numbers given to you. A timer is used, and you can either time out or earn bonus points, depending on how quickly you finish the game.
As a game that has appeal for both children and adults, "Adding Aliens" is a good choice for those who would like to improve their own math skills while sharing something with their kids. One of the best features of this particular game is that you can choose your own level. Math skills that may be a little young for adults can be skipped over by going directly to the more advanced levels. The basis of the game is that the player must shoot down alien ships by answering math problems (including addition problems) correctly. Higher levels require you to not only add more quickly to win, but also to add larger and more difficult sums.
"Choose Math Operation Game" is especially useful for those who would like to hone other math skills along with addition. A great feature on this game is that you can choose your own range of numbers that the game will test you on, which is perfect for those who want to practice adding negative numbers as most other games focus only on positive numbers. In this game, you must figure out which mathematical operations are required to create a certain number. Your goal is to help a fish jump up a flight of stairs by answering at least 10 questions correctly.