Free Y is a two-player game that is played on an initially empty hexagonal grid with an odd total number of boundary cells, preferably outlining a near-regular hexagon with odd sides one cell longer than even sides.
On your turn, place a stone of your color on an empty cell. You win if there is a group (set of connected stones) of your color such that any region (set of connected cells) outside that group includes less than half of the boundary cells.
Bill Taylor posted Free Y in 2008 on the rec.games.abstract newsgroup.