Join five

[1] In addition to being played recreationally, the game has been the subject of theoretical studies[2] and computer searches for solutions.

In the single player version, scoring is accomplished by counting the number of segments drawn, or by calculating the total area of the grid at the end of play.

Also, the "disjoint" variation of the game does not allow two parallel lines to share an endpoint, whereas the standard "touching" version does allow this.

[11] Generalized morpion solitaire, in which the starting configuration may be any finite set of marked points, is a member of the NP-hard class of problems for which no efficient computational method for finding an optimal solution is known.

[2] For the standard versions of morpion solitaire, infinitely large solutions do not exist; upper bounds have been proven[2] on the maximum number of lines that can be obtained.

The starting grid.
After one move.
After four moves.
The game ends when no more segments can be drawn on the grid.