Well, first, a lot of this stuff is actually written in Scala, which is like Java's younger and more fun cousin. Still runs on the JVM but has many fun language aspects I won't get into because there's already a billion posts online about that.

But second, not quite a "platform" but I've been enjoying Frank McSherry's blog posts in which he builds up a complete distributed dataflow engine in Rust: http://www.frankmcsherry.org/