alt Hacker NewsGraal is based on OpenJDK. OpenJ9 while using a separate JVM and JIT leverage the openjdk class path as well as the build environment and various other things.
I don’t think there’s a single alternate implementation that doesn’t leverage a good chunk of openjdk somehow
For the simple reason that class files with JVM bytecode are the standardized intermediate representation. Therefore, duplicating the frontend is wasted effort.