aspell

GNU Aspell spell-checker
GNU Aspell is a spell-checker which can be used either as a standalone
application or embedded in other programs. Its main feature is that it
does a much better job of suggesting possible spellings than just about
any other spell-checker available for the English language, including
Ispell and Microsoft Word. It also has many other technical
enhancements over Ispell such as using shared memory for dictionaries
and intelligently handling personal dictionaries when more than one
Aspell process is open at once.
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Aspell is designed to be a drop-in replacement for Ispell.