Renju

Renju is the international competitive version of Gomoku, formalised in Japan at the end of the 19th century. Both players take turns placing stones on a 15×15 board trying to get five in a row. Because Gomoku is a first-player win under naive rules, Renju adds several restrictions on Black's moves — no double-threes, double-fours or overlines — to balance the game. The Renju International Federation runs biennial world championships.