It is a meta-circular VM, where all layers except for a small glue layer is implemented in Java, already that is quite cool.

It grew out of the MaximeVM project at Sun labs.

Other well known meta-circular JVM,were Squawk for Sun SPOT and Jikes RVM.

Then on top of that, it provides a LLVM like infrastructure to build compilers and language runtimes, all in memory safe language like Java.

Additionally there is a long term roadmap to increasingly replace C++ parts of OpenJDK with GraalVM code.