Caro is a popular strategy game that is played in Vietnam. There are many variations (it is sometimes refered to as Gomoku in Japan and other Asian countries), but at its most common the game resembles Connect Four or Tic Tac Toe in that two players take turns placing their markers inside the grill. Instead of three or four in a row, however, Caro requires five to win.
Additionally, both sides of the line must be free spaces, or also owned by the same player. For instance, if a player has five in a row, but one marker from the other player is at the end of that row (_OOOOOX), they have not won. However, if the O player adds one more to his line and the end of the line is free (_OOOOOOX) the O player has won because one side is free and the other is controlled by O.
You can download the game board along here with an explanation of the rules in French. Also, for the tech-savvy, there is an application for iPhone and iPad you can download a variation of the game here.