LingoBattle, PVP Language Learning
Duolingo leagues already do ELO-ranked language learning with bigger content libraries.

Duolingo for slang when Babbel and Memrise already cover conversational language.
Adult language learners tired of textbook phrases
Duolingo · Memrise · Babbel
So I built this! Real Talk Tutor
Basically I want to see if people actually like it before I officially make it an app (also not sure about content rules on the App Store).
Duolingo leagues already do ELO-ranked language learning with bigger content libraries.
Sentence-pattern focus beats Duolingo's vocab drills for actual conversation skills.
Topic-based conversation generator when Talkpal and Lingodeer already do this.
Clean audiobook+text sync for language learning, but LibriVox and LingQ already do this.
Another AI language tutor with a progress heatmap and structured levels.
One-tap word lookup while reading beats flashcard-only apps.