SCOWL (Spell Checker Oriented Word Lists) is a database of English words that can be used to create word lists suitable for use in spell checkers of various sizes and dialects (America, British (both -ise and -ize) and Canadian). However, I am sure it will have numerous other uses as well.
The main product of SCOWL are spell checker dictionaries for Hunspell and Aspell.
SCOWL was created by carefully combing many other high quality wordlists. The creation of SCOWL also lead to many other useful artifacts.
One of the main sources used by SCOWL is Alan Beale 12Dicts package.
One of the main artifacts created was the VarCon (Variant Conversion) database, that can be used to convert between American, British and Canadian dictionaries.