Writefull is a desktop and Chrome extension that checks your writing against databases of correct languages and gives feedback on your writing.
One of its strongest points is the ability to use it with most applications. Simply select a piece of text, hit the short-key to activate Writefull, and choose one of its many options.
Check how often your selected text is found in the language database, and see how it is used in context. Hear how your text is pronounced. Translate from any language into English. Enter two chunks and compare how often they are found in the database. Also, see how they are used in context. Find out which words are used most often in a gap in your selected text. See which synonyms of a given word are used most often in your selected text.
MajorGeeks mirrors are the desktop, portable version.