Language Mentor is a) a mobile app, and b) a free and open platform for publishing language lessons.
The Humanities app currently has Chinese and German lessons available, but our vision is that as Language Mentor becomes better known more people and organizations will create lessons and eventually there will be many lessons for many languages. It's a fairly simple drill and practice app. It offers language lessons in a "mostly audio" format, so that learners can study languages while they are doing other things such as exercising, housework, etc.
We encourage authors to release their lessons under a Creative Commons license. So far (as of September 2019) all have done so. The source code for Language Mentor is open source and is available on GitHub.
We're currently working on an authoring tool that will make it easy to create lessons. Currently this requires some "geek skills" and we'd like to eliminate this obstacle. But this is currently a work in progress...
However, the Language Mentor app itself is fairly polished. You can check it out by taking a look at our website at http://languagecollaborative.com, or simply download the app from the App Store or Play Store and give it a try.