- Pre-made decks of cards on a range of subjects available on the web ("shared decks").
- Cloud storage of cards (AnkiWeb).
- Syncing reviews between platforms (desktop app, phone, web).
[0] Full disclosure - I've used Anki daily for over 4 years now on ~30,000 cards, and I haven't tried any other tools.
This is of very varied quality though. Some decks are made by university professors that teach a class on an advanced topic, and they are top notch. Other decks are simply wrong, and questionable. This especially applies to language learning, since people creating the decks aren't proficient yet.
That's why I loved Wanikani [1]. In the end, it is just Anki with some extra stuff, but you pay for the excellent quality of the content.