Perl 6 Compilers

Rakudo is based on the Parrot virtual machine. It is developed very actively. Download or compile Rakudo, status.
STD.pm is Larry Wall's reference implementation of the Perl 6 grammar, parser generator, and some of the semantic verifier. STD is an abbreviation of "Standard", as in "Perl6.0.0-STD". It is written in Perl 6, transliterated into Perl 5 by "gimme5", and supported by Cursor.pm and Moose and others.
SMOP is a runtime library to represent Perl 6 objects. It focuses on the meta object programming capabilities. It is actively developed.
Mildew uses STD.pm as a parser and SMOP as runtime. It is actively developed.
Perlito, also known as MiniPerl6, is a subset of Perl 6, designed as a light bootstrapping language. You can try it online. It is actively developed.
Sprixel uses JavaScript to compile Perl 6 to JavaScript, with a runtime written in JavaScript. Recently, an STD.pm-compatible parser-generator was being written. It is actively developed.
Elf is a bootstrapped compiler with Perl 5 and Lisp backends. Only very little activity since March 2009.
Pugs is written in Haskell, and has been inactive in the pugscode repository since mid 2007, but new releases for successive versions of ghc are published to Hackage. The most recent (6.2.13.15 as of this writing) was released 2009-12-16.