[seren]

Have you heard about Memrise? It is site/mobile app dedicated to learn new language using SRS.

Apart from official content, most of the content is contributed by bilingual users. So I don't know the quality/accuracy of them, but the result is that they have lots of courses.

https://www.memrise.com/courses/english/serbian/

It is a bit hard to pick up grammar or conversationnal skills but to learn some vocabulary it is great.

[bko]

I haven't heard of it but will definitely check it out. Thanks for the tip!