A free app for Android, by Stephan Widor.

Sudoku Scan&Solve is an app that scans and solves sudokus. It is a complete free app for all your needs.

This application is the most complete and most powerful one available in the store. You can do a lot of things with it, such as create sudokus, find numbers in a row, column, or box, or solve the whole puzzle. You can also tell it where a number is in a row, column, or box, or if you have made a mistake. You can also use it as a simple Sudoku app that always tells you if you’ve made a mistake and helps you when you get stuck.