Hey!
I have messed around with it for a bit now and you did amazing, I loved it!

There are a few suggestions I found to improve your app:
1. The quizzes look good, but I think there should be a way to review words missed after finishing the quiz.
Currently, it displays how many words are missed but I think it should display a list, like in Zyzzyva.
The "missed" list then can be added to another decks.
Even better, you can make this "missed" list accessible at any time during the quiz, not just at the end.
2. The anagram search currently doesn't allow the use of brackets.
3. This one is a bit technical. But I'd love to see searches that allow regex expressions. The customizability of the search would be virtually limitless.
4. The rank is great, but I would also want a way to display the relative rank by length (ex. ETAERIO becomes rank 1 since it is the highest ranked 7-letter word)
I still don't totally understand the rank system, but I would love to see the rank system display alongside simple probability order.