FITS (Fill In The Spaces) is essentially a multi-player Tetris. Each player has an inclined board on which they place different polyominoes, with three, four, or five squares. Cards are drawn from a pile to tell the players which piece to take. The pieces may be rotated and reversed before they slide down the inclined area to dock to other gaming pieces, but unlike Tetris cannot be slid horizontally once dropped. Scoring is based on quantity and configuration of squares left uncovered.

Unlike original Tetris there is no time pressure but like Tetris every player is engaged with his own board.