Founder here. Note: This is spaced repetition. I bootstrapped this over the past 1 1/2 years. A few key differences: - A central DB (it has over 1.8M flash cards) which anybody can edit. Card owner can accept/reject the change request. - Courses are just references to flash cards, nothing else. - You decide what you want to learn "Display me field X,Y,Z and prompt me to enter field 'A'. You can choose any field/audio…
The interesting differences between, say duolingo and what a sign student would want to see:
* Flashcards are okay for some signs but plenty of signs are much better seen animated
* some signs are complicated and you need to see the whole signer from waist up; others are simple enough a simple image would do
* Short youtube embedded clips are okay except loading times are aggravating
* clips should be high res; some finger actions are small and detail can be hard to see
* there are variations between different sign languages, eg BSL and ASL
* source material is hard to get but there are a few sign teachers working on their own, one video at a time. They might be interested in partnering.