FREE - In Google Play
FREE - in Win Phone Store
You might already know this puzzle.
yes, I know, it is known as Pearl of Poznan, played I think in 1930. What's interesting that after 2 years really similar position occured (just different pawn structure) and the player also found the solution (argentina, miguel orteta I think).
This ending is such extremely beautiful, that it is the first position and sequence of moves that I have ever remembered.