Human Solvable Zero
I enjoy creating puzzles that the computer programs (specifically JC's JSudoku and Richard's SudokuSolver) have difficulty with, whereas humans can solve them; sometimes easily.
I have posted 26 of them on the Assassin site and while thinking of the 27th I realised that I had missed the easiest one of all. Hence this human solvable zero.
It is X (but I did not use that much in my solution).
It is of medium difficulty: SS and JS both fail but after some help SS gives it 0.95 and JS does not use any fishes.
I will shortly post some more difficult variants on the assassin site.
If requested I will post my solution method.