I think Moose is a port of Perl 6's OO system back to Perl 5.

AIUI that's how it started, but to quote from Moose's docs themselves:

Is Moose just Perl 6 in Perl 5?

No. While Moose is very much inspired by Perl 6, it is not itself Perl 6. Instead, it is an OO system for Perl 5. I built Moose because I was tired or writing the same old boring Perl 5 OO code, and drooling over Perl 6 OO. So instead of switching to Ruby, I wrote Moose :)

However audreyt mentions it in her Deploying Perl 6 talk and specifically writes:

What is Moose?

• Complete object model for Perl 5
• Based on the Perl 6 object model
• Production Ready