Spline is a simple N-in-a-row game that exploits the pyramidal stacking to guarantee a winner.

The board starts empty. Two players, White and Black, takes turns placing a ball of their colour either on an empty board hole or to stack on any 2x2 platform.

Aim: A player wins by making a full line, orthogonally or diagonally, on any level. That is, lines on the 4x4 (board) level must be of length 4, lines on the 3x3 level must be of length 3, and lines on the 2x2 level must be of length 2.

The following diagrams show completed games won by White with 3-in-a-row (left) and Black with 2-in-a-row (right).

Every game is guaranteed to produce a winner before the board fills up, as any two balls of the same colour on the penultimate level (2x2) must necessarily form a line.

Spline expresses shibumi in its simple rules, intuitive nature and guaranteed result.