This is one of the N-in-a-row games. The game gird is a 3x3 set of columns, with O or X beads dropped onto them creating a 3x3x3 game play area.
As normal Tic-Tac-Toe, play alternates between players with the goal being to create 3-in-a-row. However this can be; Horizontal - all 3 on the same level, Vertical - all 3 on the same post, or Diagonal across levels and/or posts.
For 3D 4-in-a-row (4x4x4) on posts see Score Four.
For Tic-Tac-Toe played over 3 independent stacked 3x3 boards see 3D Tic Tac Toe.