This is a simple game for small children, created from scratch with the visual programming language Delphi for Windows versions 98 and later. The flexibility of a computer-based game has been exploited here with diagonal and 'jump-over' moves allowed on different levels of difficulty.

Move a tile by clicking it to make it jump into the empty space (if that move is allowed in that level) to form a crab shape. There are four different crabs to choose from. There are three levels of difficulty: Easy - where the tiles can move from any position into the vacant square. Difficult - where the tiles can only move one square, either diagonally or left/right/up/down into the vacant square. Very Hard - where the tiles can only move one square left/right/up/down into the vacant square (as in the traditional mechanical version!).
Just click a tile and it will jump into the vacant square if it is a valid move for that level.