I think that there is no better alternative to Rails to write the back-end for web/mobile applications in a very efficient and maintainable way, unless you have

I think that there is no better alternative to Rails to write the back-end for web/mobile applications in a very efficient and maintainable way, unless you have very demanding (and uncommon) requirements for performance and "web scale". I also think that the most important part which is missing to make it even more relevant is a much easier (opinionated, convention-over-configuration and DRY) way to connect rails with React and similar frameworks. Something like generators to synchronise your data with a state manager in the front end (eg Redux). I even have some ideas about this, I just wished I had time to work on it.