Vocab simply follows your progress and due to adaptive algorithms it knows which words you need to learn at the moment.
Vocab gives you control over your data, you can train many languages, organise your vocabulary into files and folders (example: lessons and books).
Vocab is available on Mac, iPhone and iPad. Your vocabulary synchronises automatically across all the devices so you can learn on the go (iPhone, iPad) or at home (Mac). It is simple and requires only Dropbox account, which you can create easily and for free.