[HuShifang]

Lingvist [0] has been useful to me for vocab building post-Duolingo. The mobile apps are thoughtfully designed -- you can use text or speech input fairly easily -- and they're rolling out (for Spanish and French so far; I'd expect German will come soon, but Russian seems to be a ways off) the ability to generate domain-inspired personalized courses using sample text you input. I'm mainly practicing my German right now, so I haven't tested it much, but this might be very powerful in combination with Project Gutenberg texts, etc. I also appreciate that they have Spanish courses for both Latin America and Spain.

[0]: https://lingvist.com/