My puzzle friend Vesa Timonen hails from Finland. He recently sent me a link to his FREE game Divisium - 3.
The object is to put up walls in order to create cell groups of 3 numbers whose sum is 3. Quite simple to learn.
Look at the image above. Each of the 40 puzzles has exactly 1 solution.
Look at the second image that's almost solved. Trying to shift walls to get that lone 0 with the other 0 & 3: quite difficult. In the end I had to just restart it.
I think level 37 took me the most time. Not sure. Altogether, I'm guessing I spent about 4-5 hours on all 40 levels.