You might want to check out Groovy. It's built on the JVM, you can use all the standard library and third party Java packages including stuff off Maven, and you can even just run straight Java code through it. However, at any time you can also drop into Groovy land, and write in a much more concise and functional style. Closures are very common (just look at anything in Gradle), it was clearly influenced by Python/Ruby as far as syntax and type optionality, there's a REPL (groovysh), there's a modern web framework (Grails), all in all it's pretty nice.
There's a learning curve, can't hit the ground running as you can with Groovy, but with Groovy there's a ceiling; with Scala the only ceiling is (perhaps) Haskell and for that you have to leave the JVM.
Languages where you can "hit the ground running" always have a ceiling. If you churn out working code quickly, you're offloading the real work onto someone else in the future. Real world programming, like business, is all about borrowing from the future, intending to default on the debt.