We play math war daily. It’s pretty similar to regular war, except you remove the 10s and face cards. For basic facts you draw two cards each instead of one. For addition and multiplication the highest answer wins, for subtraction and division lowest card wins.
We also play it to practice two (or more) digit addition and subtraction, as well as column addition. We have also recently begun using it for practice with multiplying larger numbers and I know there’s a way to do it with fractions, but I haven’t learned that version yet.
This has been a very helpful tool for my ds, who could potentially take hours to finish a worksheet, because it keeps him focused and on his toes. 🙂