> They are using an xml based format which can be extended to anything.

Oh, I didn't know this part!

>> But, not everyone uses flashcard programs only for plain vocabularies.

>What for then? Can you give us examples?

Well.... I sometimes need to use them for mathematical formulas, maps and almost everything I want to learn!

>I think Parley can easily be extended too

It seems Parley is using a richer library than I thought! and it has the potential to improve a lot. That's great ;)