SlackBuildsOrg/office/anorack

The English language has two indefinite articles:

  a: used before words that begin with a consonant sound (e.g., a
     program, a host, a user);
  an: used before words that begin with a vowel sound (e.g., an example,
      an hour, an undefined variable).

anorack is a specialized spell-checker that finds incorrect indefinite
articles.