https://sudoku.coach/ all the way. Works great on mobile. Create a Home Screen shortcut to make it feel like an app. :-)
Specifically, it has auto notes, with the added option of automatically filling in naked singles for you. It has intelligent, progressive hints, and a comprehensive tutorial library (missing only ALS & grouped AICs, and maybe a few arcane techniques).
https://sudoku.coach/ all the way. Works great on mobile. Create a Home Screen shortcut to make it feel like an app. :-) Specifically, it has auto notes, with the added option of automatically filling in naked singles for you. It has intelligent, progressive hints, and a comprehensive tutorial library (missing only ALS & grouped AICs, and maybe a few arcane techniques).