Side by Side by von Guenther Rosenbaum looks like a Sudoku, but it's not.
  The object is to fill the grid with either numbers 1, 2, 3 or 4 or an X.  A few simple rules: each number represents how many adjacent (horizontal & vertical) squares have numbers. Adjacent squares cannot have the same number.  All the numbers have to be connected.
I have done about 10 levels in the 6x6 grid.  The grid sizes go up to 15 x 15..  Very polished.
http://www.rosenbaum-games.de/sw/sidebyside/index.htm
https://itunes.apple.com/de/app/side-by-side-game/id990437059"mt=8&ign-mpt=uo%3D4

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