Questions, problems and suggestions all go to one address: danchap@gmail.com. You will get an answer from the person who makes the app.
The course is a list of flashcard decks in order, from the first words to C2 and beyond. You add a deck, its cards land on the top level of the cascade, and each time you get a card right it drops a level, with a longer wait before the next review. Miss a card and it goes back up. The app does not listen to you: you say the answer, tap to see it, and judge yourself. The guide inside the app, the question mark at the top right, walks through all of this.
There is no account and no sign-in. The app creates a random identifier the first time it opens and keeps your progress on our server under it. On iPhone the identifier is also kept in the device's keychain, so your progress comes back after a reinstall, and iCloud Keychain can carry it to your other iPhones.
Reviews work without a connection: the cards you have added are on the phone, and your reviews sync when you are back online. Adding a new deck needs a connection.
Resetting the cascade inside the app returns every card to its deck. To have everything tied to your identifier deleted from our server, email the address above from the app's menu or any mail app, and it will be removed.
The privacy policy says what the app stores, which is nearly nothing. The same course runs in the browser at cardcascade.com.