Atom-4 is a two-player color manipulation game played with colored spherical pieces on a board divided into equilateral triangles. The player who first makes a row of 4 pieces of the right color wins. However, the players do not directly play pieces of the winning color; they must construct their winning pieces via color changes that happen to neighbouring pieces whenever a new piece is placed on the board.

Atom-4 supports both a curses-based text interface and an X11 interface.