Naughts and Crosses is a great game to play with your students, simple and easy to set up. But, it only works for two teams and isn't terribly visually stimulating.
Car Park is just as good, if not better! It works really well for three teams, it's easier to set up than traditional Naughts and Crosses and it looks a lot better!
Split your class into three teams and assign each team a coloured car (green, blue or yellow). If they answer a question correctly they can park their car in a parking space of their choosing. If they are the green team, they click on the top of the parking space. If they are blue, the click in the middle of the space. If they are yellow they click on the bottom of the space. Their car will then park in that space.
The aim of the game is to get three cars of your colour in a row, either horizontally, vertically or diagonally!