This is a variant of Hexagonal Chess by W. Glinski - a variant designed for three players.

Each player starts from his own board corner of the hexagonal board (120 degrees from his rivals). Rules of pieces movement are the same as in two-player version (with the exception that there is no main front-back board axis but every player has his own one determining pawn movement). The player who checkmates any of the enemies' kings wins, the checkmated player and the third one (a.k.a. "observer") both lose.