The first sliding block puzzle was invented in the 1870's. It was THE "15". America's greatest puzzle expert, Sam Loyd,"drove the entire world crazy" (as he himself put it) with this newly invented puzzle.

"THE 15" is one of the most interesting intellectual games in the history of mankind" - these are Rubik's words and each of us will certainly agree with them. However, while playing  "THE 15" you had the feeling of a certain incompleteness, didn't you? The reason is the vacant cell which, indeed, should be filled in by the sixteenth block! But it is impossible, you will say, the blocks will then loose their capacity to move! Yes, of course, if they are placed in the box ...
But what if that is not the case?
Our puzzles are based on the rectangular elements - blocks situated within one plane.
Blocks are mutually coupled, any boxes or frames are absent. Blocks are capable of moving in relation to each other by rows changing their places. The number of blocks is not limited, the most reasonable sizes of the game are 4x4, 4x5, 5x5.
Both sides of blocks are active and may have different pictures. There are versions of colors (marking) transforming the puzzle into a game for two players.