Squava is a derivative of Yavalath with the same goal but different components. It is intended to be a small simple game that can be played with pen and pencil, or with stones and shells on the beach.
It is played on a 5x5 square board (though you can probably play it on a 6x6 to use all the Green Box tiles). 2 players alternate turns placing a piece of their colour on an empty space of the board.
Players win if they make a line of 4 pieces of their colour, but lose if they make a line of 3 before doing so. Lines can be orthogonal or diagonal.
Links:
BGG: Squava
BGG: Yavalath