Four Strikes
A great math game from Marilyn Burns, especially for grades 2-4. http://www.marilynburnsmathblog.com/four-strikes-and-youre-out/
It's like Math Hangman. You try to guess the digits in an equation before you get 4 misses.
This one has an option to make it harder by choosing less than four strikes before you hit new for a new game.