Right now rakudo with MoarVM is for all intents and purposes the main implementation of Perl6. The rakudo frontend also works with the JVM. There's work to make

Right now rakudo with MoarVM is for all intents and purposes the main implementation of Perl6. The rakudo frontend also works with the JVM. There's work to make it work with JavaScript as a backend. It is in a continual state of being really close to the latest spec, but right now the spec is undergoing versioned revision too. Niecza is an implementation of Perl6 which targets the CLR. Last I checked it lagged rakudo a bit but was still being updated and maintained. There are other, independent implementations of Perl6. There's STD.pm which implements Perl6 in Perl6 and uses viv to transliterate portions of itself into Perl5. Pugs is last I checked dormant, but it was an independent implementation of Perl6 in Haskell. So if someone asks for an implementation of Perl6, they probably want rakudo. Just like if someone asks about an implentation of Ruby they probably want CRuby / MRI unless they for some reason don't. Ruby, however, doesn't really have a language spec so other Ruby implementations like JRuby chase MRI compatibility. This was a problem with Perl5 which was defined by its primary implementation. Python has the Python Language Reference for alternate implementations like IronPython and Pypy to develop against, much like the R5RS and R6RS Scheme documents. This is why Perl6 the language is defined by the spec - so multiple implementations can compatibly exist.