ZudokuPuzzo

This app provides innovative tools that simplify the solving process.
It comes with a tutorial that guides you through the process in a few simple steps.

Some definitions:
A Cell is one of the 81 small squares.
A Box is one of the 9 3x3 grids.
A Unit refers to a box, a row, or a column.
The Peer of a cell is the collection of the 20 other cells in the cell's three units.

To solve a cell, you just need to know the A-B Rules.

A-Rule: If a blank's peer contains eight different digits, the missing digit is the solution.
Help: The Input Bar automatically removes all the candidates that are in its peer so you do not need to worry about entering an invalid digit.

B-Rule: If one of the valid candidates in a unit is found in the peers of all but one blank cells, that digit is the solution to that blank.
Help: Each button on the Unit Bars around the grid corresponds to a Unit.
Tapping a button shows the blank cells in cyan on the unit displays the valid candidates on the Brown Bar.
If more help is needed, just tap a digit on the Brown Bar.
The peers of all the occurrences of that digit are shown in pink.
If only one cyan cell is left, the digit is the solution to the cell.

Other tools include Hint, Branch, Backtrack, Check, Reveal, Erase, Lock, Unlock and Undo.

There are additional 15 character sets to try if you'd like to use something other than regular numbers.