I'm churning out code to turn its installer, Pyrus, from vaporware into actual code. Along these lines, there has been significant progress. The code has been developed on PHP 5.2, but will most likely target PHP 5.3 with the introduction of namespaces. Pyrus completely revamps the way things are done.
Greg mentions some of the functionality the installer will use including XMLReader/XMLWriter, namespaces and bits of functionality from the Standard PHP Library (SPL). He's released what he's developed so far via a PEAR channel with no other dependencies.