Ispell

Ispell is a spelling checker for Unix that supports most Western languages.

Unlike GNU Aspell, ispell will only suggest corrections that are based on a Damerau–Levenshtein distance of 1; it will not attempt to guess more distant corrections based on English pronunciation rules.

The generalized affix description system introduced by ispell has since been imitated by other spelling checkers such as MySpell.

Ispell then attempts to generate a list of possible corrections and presents the incorrect word and any suggestions to the user, who can then choose a correction, replace the word with a new one, leave it unchanged, or add it to the dictionary.

Ispell pioneered the idea of a programming interface, which was originally intended for use by Emacs.