西瓜棋 (xī guā qí́), or Watermelon Game, has been described as a traditional folk game from Hangzhou for children. The set I have was purchased from a toy shop in Shanghai.
Xi Gua Qi is played on a board that vaguely resembles a watermelon. It is a game of abstract strategy and the object is to capture the opponent's pieces by immobilization. Each player starts with six pieces and moves them from intersection to intersection on the board. If you succeed in surrounding an opponent's piece with your own pieces, it is removed from the board. The winner is the player who reduces his opponent to less than two pieces.
The game is available as computer software by Locke Corp for the pocket PC.