Anki — Friendly, intelligent flash cards. Remember stuff.

anki is great!

I use it for a long time now. And you know what? I speak 8 languages by now. Not counting the programming languages, only the natural ones. And I use ANKI for everything, not only that!

Pros:

Spaced repetition is the best scientifically confirmed way to remember stuff you need to remember. And here you choose what to remember!

Cons:

No cons. May be the interface could be a bit more flahy but I personally do not care.

Best language app ever, I've been using it for years.

iOS version, web version, friendly UX