I know this thread is absolutely ancient, but for other people who might be searching, no there isn't exactly a good Renshuu app equivalent for other languages but there are some that are close enough, typically websites.
For German, for example, the news corporation Deutsche Welle has a free Learn German course on their website that'll take you all the way to C2.
For French, there's a free site called Lawless French that has a lot of great lessons ranging from beginner to C2.
There's also a company called Akelius Languages that have about a dozen completely free language courses on their website (there is an app but it's hideously slow so I recommend the website). Akelius actually partner with Unicef to teach their language courses to refugees around the world, so the quality is good.
Anki will also always be one of the best resources – there's so many decks now that don't just train vocab, but will also have grammar tips, audio, pictures, etc.
It's not the same style, but depending on where you live you might be able to access Mango Languages for free through your local library (unfortunately I can't, but I've heard extremely good things about it).
Otherwise, Renshuu definitely seems to be a bit of a special case. Still, you're probably not going to find a good app, but there are plenty of good free websites out there still for a lot for different languages.
