4. Spellcheckplus.com

This is a great spelling and grammar checking program. It is free, but the number of words you may add is more limited. You can pay a small yearly fee to increase the number of words. The great thing about this tool is that it picks up on potential typo mistakes. It picks out the less obvious mistakes that are easy to miss when you are proofreading and is a better performer than most built-in word processing spell checkers