"Metascala is barely 3000 lines of Scala, and is complete enough that it is able to interpret itself metacircularly. [...]

The goal of Metascala is to create a platform to experiment with the JVM: a 3000 line JVM written in Scala is probably much more approachable than the 1,000,000 lines of C/C++ which make up HotSpot, the standard implementation, and more amenable to implementing fun features like continuations, isolates or value classes."

That seems pretty neat to me.