You might be interested in this site.
Sudoku Online : Sudoku of the Day
I have found this site instructive and the software easy to use. However, I do not usually use it unless I have a puzzle I cannot complete after several tries. The program helps understanding of patterns to look for.
Sudoku Susser – Freeware Sudoku Solver & Assistant for Macintosh and Windows (Projects)
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I enjoyed the sight if you want some good sites I know a few
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