I am on holiday without Windows, so also without SiSeSuSo, my solver or SudokuExplainer...
On the Android app store there was a LogicWiz Sudoku app with lots of variants.
No overlapping multiple sudokus, but more variants than I expected. Including multiple variants in one sudoku puzzle.
Very good for manual solving. I got completely addicted.
And in airplane-mode the advertisements are omitted.
Great app to be recommended here. Very nice control panel.

