This is a handy free tool that also has a downloadable desktop app for proofreading your work. It has some understanding of context and so can analyze errors which may otherwise be missed. Very useful tool.
Flashcards Deluxe is an easy to use, yet powerful flashcard app which you can use to study just about anything you want. I use this app for my own Chinese studies, and am constantly improving it to make it better for myself and others.