I wrote this PvP GOMOKU game in Java, using socket for local network communication.
局域网对战的五子棋Java程序。
You can run the pre-compiled version (GOMOKU_GUI_Socker.jar) directly.
To play, you need to have a host running on one computer, and a client running on the other computer. The host and client should using the same local network. At the client side, enter the local IP of the host computer. Then you can start the game (P.S. host need to make the first move)!