Homepage: aspell.net.
aspell check document.txt # interactive correction (backs up as document.txt.bak)
aspell list < document.txt | sort -u # list misspelled words only
aspell -l en_CA list < document.txt # choose a dictionary (see: aspell dicts)
echo "recieve" | aspell -a # pipe mode: suggestions for words on stdin
Add --mode=html or --mode=markdown to skip markup when checking web or documentation sources. Related: dict.