Four in a line

This is one of classic pen-and-paper games. This task is to implement
a client application and a server hosting any number of games. It is
a server's responsibility to pair clients and check when the game ends.
For each pair of clients, the server creates a separate thread. All
communication is realized by TCP sockets. After connecting to the server,
a client can list existing games - both paired and unpaired, player nicks
and game board size. Then, the connected client can choose to watch
an existing game, connect to other unpaired client and start the game or
create his own game. Clients are not paired automatically. When a client 
creates a game it chooses a nick and game board size (varying from 4 to 
20). When a client is connected, a board is displayed with the current 
game state. During the game, clients in a pair can chat privately with 
each other. After the game client is not disconnected, it can start 
all over again.