Dozo (1970)

Dozo is one of Stancraft's line of puzzles and abstract games under the "Hoyle Official Games" line (the company may or may not be the same one called "Hoyle Products" a few years later). Dozo consists of a board with 28 spaces in an equilateral triangle and 7 Go stones in each of 4 colors. On a turn, a player places any color stone on the board. The object is to be the first player to place a piece which forms the third vertex of an equilateral triangle with 2 other pieces of the same color.