Duolingo (iOS)
Used by 8 peopleapps.apple.com ↗

“I've been having a great time learning German in Duolingo.”
Nathan Hoad Interview, Interactive developer, artist · via Uses This 
“I want to use apps like Duolingo more regularly, to help me get started in French and level up in German (specifically, its grammar).”
Meredith Forrester Interview, Copy editor (The Good Copy) · via Uses This 
“I've been on a Duolingo kick lately, my girlfriend is Colombian and I've been learning Spanish, it's going pretty well.”
Vivian The Dog Interview, 6-foot tall dachshund · via Uses This