One Letter Different
One Letter Different will find any entries in the lexicon that differ from the entered pattern by only one letter.
For example, given the word "much", changing the first letter yields "ouch" and "such"; changing the second letter gives "Mach"; the third and fourth letters, "mush" and "muck", respectively.
See also Multiple Characters and Ranges.
The software that drives the WordFinder is a collection of Unix shell scripts. Most of these scripts are available in my book, Shell Scripting Recipes: A Problem-Solution Approach (Apress, May 2005). You can run these scripts on any version of Unix, including Linux, Solaris, and the various BSD implementations. They have not been tested on Mac OS/X, but they should work there, too. (If you try them, please let me know how they run.)