When we started the Perl 6 Advent Calendar back in 2009, Rakudo was really the only game in town if you wanted to play with Perl 6. But Perl 6 was intended from the start to be a language with multiple implementations, and at the moment there are four different Perl 6 implementations of interest. Because there are so many implementations, I’m not going to give instructions for getting each; instead I’m linking to those instructions.
The most stable and complete implementation is Rakudo Star. This is currently based on the last major revision of Rakudo. It’s been frozen since July, and so lags a bit behind the current Perl 6 spec. It’s slow. But it’s also pretty reliable.
The current Rakudo development version is called “Nom”. It’s full of great improvements over the last Rakudo Star release, notably native types, improved performance, and a much better metamodel. (For example, check out the Grammar::Tracer module, which takes advantage of the new metamodel to add regex tracing in just 44 lines of code.) It’s not quite ready for prime time yet, as it still misses some features that work in Rakudo Star, but progress has been incredible, and it’s quite possible a new Rakudo Star based on Nom will be released during this month.
Stefan O’Rear’s Niecza was just a fledging compiler during last year’s Advent calendar, but it’s a serious contender these days. Built to run on the CLR (.NET and Mono), it is relatively zippy, implements a significant portion of Perl 6, and works easily with existing CLR libraries.
Lastly, ingy and Mäsak have plans afoot to revive Pugs, the original Perl 6 implementation in Haskell. So far they’ve just got it building again on current Haskell compilers, but the long-term goal is to get it running on the spec tests again and bring it closer to the current spec.
Which implementation should you use? If you’re looking for a stable, fairly complete Perl 6, Rakudo Star is it. If you just want to explore the language, try Rakudo Nom — you will probably run into bugs, but it’s significantly more advanced than Rakudo Star, and exposing the bugs is a big help to Rakudo’s development. If you have an idea which would benefit from being able to use CLR libraries, Niecza is fantastic. There’s a handy comparison chart of the different features available.
Personally, I have all three of these installed on my machine, and have different projects underway on each of them.
Finally, please don’t hesitate to ask for help, either in the comments here or on the #perl6 IRC channel on Freenode. The Perl 6 community is very friendly.
Raku Advent Calendar (2009-2019) 
Colomon++.
I love the fact there are so many serious Perl 6 implementations. There will be those who claim balkanization etc., but *.
Here’s another implementation that might be interesting to some others that I just saw posted about somewhere else (I forget where). I took a quick gander. Here’s a brief summary: online test page: http://perlcabal.org/~fglock/perlito.html; on github, first checked in a couple years ago, plenty of commits in last week; most of the project pages (eg perlito.org) seem out of date. For most of its life Perlito was labelled as a P6 subset; don’t know if the recent dropping of the subset label is deliberate or not, meaningful or not.
And then there’s NQP (“not quite perl”), which is very deliberately a P6 subset.