Perl 6 for Perl 5: Revision 4
Incredibly, an effort lead by Flávio Soibelmann Glock is working to actually implement Perl 6 in Perl 5. You can download v6 now on CPAN to try it out. It's feature set has not caught up with pugs yet, but there is steady progress on it.
Perl 6 features are also coming to Perl 5 in other ways. As described below, a number of Perl 5 modules already implement some Perl 6 features, and some aspects of Perl 6 are being added to the official 5 releases, starting with Perl 5.10.
Perl 5 modules implementing Perl 6 features