Welltris

Welltris is a puzzle video game developed by Doca and licensed to Bullet-Proof Software. It is an official game in the Tetris series. Adaptations were made by Sphere, Inc., for Spectrum HoloByte, and by Infogrames. It was released in 1989 for MS-DOS compatible operating systems.

Welltris was the first sequel to Tetris, designed by original designer Alexey Pajitnov, together with Andrei Sgenov. It retains that game's falling-block puzzle gameplay, but expands the pit into three dimensions while keeping the blocks two-dimensional, with the board seen from above.

As blocks descend into the pit, they can be rotated or moved left or right along the walls as desired, from one wall to another. Once a block reaches the floor, it slides as far as possible until it is stopped by an edge or other piece. Each time the player completes a continuous horizontal or vertical line, it disappears and the remaining squares slide to fill the open space.

If a falling block comes to rest with part of itself still resting on a wall, that wall is temporarily frozen; During this time, no blocks can be moved to it. Freezing all four walls ends the game.