A game of Four in a Row that travels by post. Each postcard carries every move so far, a picture of the board, and one line in your own handwriting. Nothing is kept here: the cards in the drawer are the game. A game takes a few weeks, and the cards are worth keeping afterwards.
The game so far
Grandpa to play (X).
The postcard
Four in a Row, by post
Moves so far: none yet
Your line:
Columns are numbered 1 to 7 from the left. Copy the moves onto your reply and add yours at the end.
Prefer a screen? The Long Game plays chess one move a day, and Four in a Row plays across the table.