The objective is to arrange the coloured/numbered blocks to match the pattern on the right hand side, in the fastest time possible. You can only move a block if there isn't one above it. You can only drop a block into a free spot. There are 3 spare spots on the right hand side to place the blocks into temporarily while moving them around.
As you move a block over a space, when the space turns green you can drop the block and it'll snap to position. If there's a free space under the one you dropped the block into, the block will slide down.
History: Numberstacker is based on an old game called Number Rhumba, whereby 2 players would each have a small frame with 4 perpendicular poles coming out of it. 9 different blocks (3 sets of different colours, which each block in a set numbered between 1 and 3) with holes through their middles were arranged on the first 3 poles. Each player would be given a card on which a jumbled pattern for the blocks would be displayed (each player got the same pattern). The object of the game was to arrange the blocks to match the pattern as fast as possible. When moving a block, you couldn't simply leave it on the table, you had to place it on the spare pole. The spare pole could also only take a maximum of 3 blocks, so you needed to plan your moves while trying to achieve the required pattern.
This game is an attempt to recreate the above, but for one player in a race against time.