Crossline is a mathematical game published in the october 2009 issue of Games Magazine. It's a pencil and paper game between two people.

Players begin by drawing a circle with ten dots evenly spaced around it (the spacing can be approximate).

The first player starts by drawing a straight line connecting any two dots that are not adjacent. After that, each player in turns draws a straight line that connects any two dots and that crosses exactly one (and only one) previously drawn line.

The player who draws the last legal line is the winner.