Each player needs a different coloured pen. Draw a 7 x 7 grid on your whiteboard and take it in turns drawing circles in the grid’s squares to create a row of 4.
Once the bottom line is filled, circles can be dropped on top, but circles cannot hover in the middle of the grid.
The first to 4-in-a-row either horizontally, vertically or diagonally wins the game!
You could also use double-sided counters, or anything that fits in the grid.