[Gregg Bell]

I'll second the vote for Balbolka. And I don't know if it was mentioned or not but when the word is spoken aloud the text for that word is also highlighted.

Now I use Linux and there is a similar program to Balbolka named Espeak.

I use the LibreOffice spell checker but I also find it helpful to borrow a Windows computer and use the Word spell checker. (I find that the Word spell (and grammar) checker catches things Libreoffice doesn't like):

John went to the store fro a gallon of milk.