Piece Puzzles app for iPhone and iPad

A sliding puzzle, sliding block puzzle, or sliding tile puzzle is a puzzle that challenges a player to slide usually flat pieces along certain routes (usually on a board) to establish a certain end-configuration.
The fifteen puzzle is the oldest type of sliding block puzzle. It was invented by Noyes Chapman and created a puzzle craze in 1880. Sam Loyd is often wrongly credited with making sliding puzzles popular based on his false claim that he invented the fifteen puzzle.
Unlike other tour puzzles, a sliding block puzzle prohibits lifting any piece off the board. This property separates sliding puzzles from rearrangement puzzles. Hence, finding moves and the paths opened up by each move within the two-dimensional confines of the board are important parts of solving sliding block puzzles.
Sliding puzzles are essentially two-dimensional in nature, even if the sliding is facilitated by mechanically interlinked pieces (like partially encaged marbles) or three-dimensional tokens. As this example shows, some sliding puzzles are mechanical puzzles. However, the mechanical fixtures are usually not essential to these puzzles; the parts could as well be tokens on a flat board that are moved according to certain rules.