ispell is described as 'Ispell is a program that helps you to correct spelling and typographical errors in a file. When presented with a word that is not in the dictionary, ispell attempts to find near misses that might include the word you meant'. There are five alternatives to ispell for a variety of platforms, including Linux, Online / Web-based, Windows, Mac and iPhone. The best alternative is Druide Antidote. It's not free, so if you're looking for a free alternative, you could try Hunspell or GNU Aspell. Other great apps like ispell are myspell (Free, Open Source) and Enchant (Free, Open Source).
GNU Aspell, usually called just Aspell, is a free software spell checker designed to replace Ispell. It is the standard spell checker for the GNU software system. It also compiles for other Unix-like operating systems and Windows.