Clonium

A board of cells that each hold a few pieces, and a turn that consists of adding one piece to a cell you own. When a cell fills, it bursts and throws a piece into each neighbor, converting them to your color — and if those neighbors were also full, the burst keeps going. Clonium is therefore a game about building a position that is one move from collapsing in your favor, and most matches are decided by a single chain that nobody saw coming until it had already crossed the board.