This is a theme for opencore (http://coactivate.org/projects/opencore).
To use it, configure your front-end proxy to hit Zope at the following URL: http://localhost:<port>/VirtualHostBase/http/<hostname>/++skin++avata/<instance>
... where <port> is the port that Zope runs on, <hostname> is the public hostname at which people visit the site, and <instance> is the name of your opencore instance (by convention this is normally "openplans").
Note that you really do need to configure your front-end proxy to hit Zope at that URL! Visiting http://localhost:<port>/++skin++avata/<instance> directly will not work, because all the css and image links will still be pointing at the unskinned site root.
It should be possible to instead use the zcml browser:defaultSkin directive, but for some reason I'm told that doesn't work with this skin.