I mean you get Hotspot on regular OpenJDK, Amazon and Microsoft OpenJDK forks have their own JIT downstream changes, Falcon on Azul, OpenJ9, PTC, Aicas,...

Azul and OpenJ9 additionally have server JITs, which widen the abilities of optimisations are available.

Additionally the ART cousin also does its own thing.

Each JVM implementation has its own approach how to do auto-vectorisation or mark intrinsic methods.

It is no different than talking about Ada, Fortran, COBOL, C, C++ and co compilers versus what ISO defines in the language standard.