Using it with spark. Scala for spark is one of the biggest production use case for scalable.
I am not clear on the meaning of the question. Are answers about domains where Scala is applied or about tooling and configuration important?
You can answer it in any way you'd like. I am interested in how others are using Scala!
For better or worse, my answer is that I don't use Scala. The development environment did not really appeal to me when I tried it a few years ago. Though I can see why people like it.