Howard Garns invented "Number Place," today known as Sudoku.
I wrote the HowardGarns program to replace pencil and paper (and eraser) while you solve Sudoku puzzles.
You can execute HowardGarns, through Java Web Start. You should receive a warning that my certificate is untrusted, because it is self-signed. Sun may also need to download the latest version of Java.
The HowardGarns program is Open Source, and is hosted at SourceForge. See the HowardGarns project page.
Use File/New to enter the numbers for the puzzle you want to solve. Puzzles are not generated by the program; you need to get them from some other source.
Here is a simple puzzle to get you started. Just select the numbers below, Ctrl-C to copy, then run the program, Ctrl-N for New, and Ctrl-V to paste.
100000239 204000000 003506400 040002160 680300002 009800007 000209600 060000005 408000900
You should look at other web sites for games in this easy text format, so you can just copy and paste. Otherwise, you can manually enter the numbers for each square, using zero for the empty squares. (You will be entering 81 numbers.)
Each square on the board shows the remaining possibilities for that square. Left-click to eliminate a possiblity after you have logically determined that that number cannot appear in that square. Alternatively, right-click on a possibility to affirm that that square does indeed contain that number.
The Solve menu lets you have the program do some of the rote logical patterns, such as eliminating possibilities from the same row, column, or box as an already identified answer. The different solvers are listed under the Solve menu; you can check the ones you want to have enabled, and uncheck the ones you want turned off. There are two ways to have the program solve for you: manually or automatically, which you can choose at the top of the Solve menu.
Manually means that you choose "Solve" from the solve menu when you want the program to apply the (check-marked) solution patterns.
Automatically means that the program will apply them after every move you make. Note that this may lead to some confusing results, in which case you may want to try turning off the automatic solving.
The program provides undo and redo support, under the Edit menu. You can undo all your previous moves, or redo them again up to any point.
You can use File/Save, Save As..., and Open..., to save and resume the puzzle. All your moves are saved, from the initial puzzle state up to the current state of the puzzle. The file is a text file. Each move also has the time the move was made saved with it.