https://lingonaut.app/
I'm really rooting for this project; it has a lot of promise. It's crowd-sourced and plans to be ad-free.
If you're more curious about details and future plans for the app, the creator did an AMA on Reddit recently.
It's not clear if the developers are simply trying to build a free alternative to Duolingo, but I'm not a fan of that approach anyway.
I tried Duolingo, but it was really just a flashy form of rote memorization. I had much greater success using Language Transfer, which is also free but is a series of MP3s.
Maybe this could be used in conjunction with LT, the former for vocabulary and the latter building up grammar and processing skills.
Yeah, I'm not sure how similar it will be to Duolingo, but the creator stated that it will include teaching grammar, which would already make it better than Duolingo.
I'm also not a huge fan of Duolingo, but I do use it because the language I'm trying to learn doesn't have a lot of great free options. However, Lingonaut will have it, so I'm looking forward to it.
Language Transfer seems really cool. I wish I could try it, but their courses don't include the language I'm trying to learn. Which language did you use LT to learn?
I have been learning Spanish with Language Transfer. My wife has too, and even though she does not have much of a gift for languages, she found it very intuitive and rewarding.
For those of you who haven't looked at language transfer, it has Spanish, Greek, Turkish, Arabic, French, German, Swahili, italian, and music theory. Some of those are introductions, others are full courses.