I was thinking it'd be pretty convenient if there was a feature to print flashcards. Maybe for each lesson there could be a button to print all the words you learned, and perhaps a line where you could add your own notes. There could be a default size and amount printed per page (maybe 4x10), with lines separating each box where you could use a scissors to cut them individually.
Just my thoughts. I imagine it'd be a relatively easy feature to add, and it'd only attract more people to your website.