I've developed a multiplayer sudoku app: https://sudoku42.xyz (play store).
It contains a precompiled list of 50 (open source) sudokus with starter and solution grouped into 4 levels of difficulty, so there's no solver or generator involved.
Its unique selling point is that you share the link with others and then start to play the same game on the same board and all moves are updated in real time. Once finished the score of all players are listed with the actual playtime.
Score is simply calculated by: correct move 1pt, wrong move -1pt, correct removal 1pt, wrong removal -1pt.
Let me know if you like it!