Sudoktor

Sudoktor is a Sudoku solving assistant. It helps you to solve and understand Sudoku puzzles but it can also be used to create and solve unlimited Sudoku puzzles.
See the support page for more details and screenshots.
App's key features:
- generates valid 9x9 sudoku puzzles of any choosen level (from easy to fiendish)
- allows to rate objectively the difficulty of the current puzzle
- allows to enter to enter standard 9x9 Sudokus manually or by copy-and-paste
- offers an intuitive and quick entry method
- shows or hides pencil marks, updates them automatically
- full Undo/Redo feature
- offers advanced analysis on demand:
- candidates
- wrong values
- solution
- subsets, grid analysis, forcing chains, almost locked subsets...
- ability to save and to reopen the games