(Shameless plug at the end)
During my Erasmus in Germany, I've tried almost all of the top language learning apps (Duolingo, Babel, Seedlang, Anki...) and none of them have really worked me.
What I wanted was:
* Learning in context --> A lot of German words do not have direct English/Czech translation, so learning the 1:1 word translation did not work well
* Having audio for each card
* Intensive pace --> Going through a lot of cards in one session. Duolingo is the worst in this as you spend a lot of time doing super easy childish exercises. If I want to learn let's say 30 min a day, I want to pack as much content as I can into it.
* Skipping ahead --> My level is around B1/B2, I don't want to do placement tests and then re-learning the words I already know
* Learning from my content --> I like to consume German podcast/youtube videos/websites and in some apps, it was quite difficult or impossible to add words I've just encountered "in the wild".
Anki has worked the best, but generating cards with sentences and audio was quite cumbersome and (a seemingly minor detail) I was loosing flow while thinking whether I knew the card "well", "good", "easy" or whatever the options are. What I like better is a simple knew/didnt know, while still using spaced-repetition.
So for the past year, I'm on-off working on a language learning app, currently only supports German, which helps you extract words from content (youtube, web, text), handles different word forms, and then generates cards with infinitely many sentence examples through GPT4, with a nice audio (latest GCP model).
The project website with Android and iOS links: https://vokabeln.io/ (web design is old, app looks very different now)