Tris combines some of the ideas of Tetris and Connect 4, with the further idea of pushing stones and them falling. It is played on a chess board, and players alternate either placing stones or moving them. Place stones can be placed on either edge, or a at the top of a column of stones from an edge. Stones can be moved one space left or right into an unoccupied space, and if it is unsupported, they "fall" to the bottom. Four stones in a row of your color are "captured" and removed from the board, the remaining stones "fall", and if more 4-in-a-rows result, this recurses. Stones in a full row are locked. Winner is first to capture 12 of their own pieces, or to fill their side of the board with locked rows.

Full rules at: http://www.luchacabra.com/?p=37