The "Download Now" link directs you to the iTunes App Store, where you must continue the download process. You must have iTunes installed in order to open the link, and you must have an active iTunes account to download the application. This download may not be available in some countries.
Each game piece has 4 unique attributes: Tall / Short, Light / Dark, Square / Circular, or Hollow / Solid. Players take turns choosing a piece which the other player must place on the board. A player wins by placing a piece on the board which forms a 2x2 square, 4 corners, or horizontal, vertical, or diagonal row with all pieces sharing a common attribute (all short, all circular, etc.)