I've been living in Montreal now for the last couple of years and have struggled to find people to practice speaking French with, so I created a web app to talk with an AI to improve my conversational skills [1]. I launched a few months ago and am seeing a little bit under $500/month in revenue so far.
I initially started by offering the service for free, but it eventually became too expensive to handle by myself. I then decided to switch to a paid and free tier and by that point I had amassed enough of a user base that a decent handful signed up to the paid tier. I optimized for user growth > revenue in the beginning because I kept thinking, "if people are not going to use this for free then they surely are not going to pay for it".
Anyhow, it's called Proseable and it also supports English, Italian, German, and Spanish!