Sliding Block Puzzles
Drag a block to slide it into an empty space, shown in white. Each puzzle has its own objective (for example, moving a block to a specified position or joining pieces with matching colors). The Demonstration indicates when you have solved the puzzle.[more]
Ten of the puzzles are classics selected from Hordern's Sliding Piece Puzzles  (which also contains their optimal solutions), and the remainder were designed especially for this Demonstration.[less]
 E. Hordern, Sliding Piece Puzzles, New York: Oxford University Press, 1986.