jrbriggsYAK for WordPress (open source, shopping cart plugin) version 1.2.3 has just been released.
There are a number of new features in this release, but top of the list are support for the Authorize.net payments gateway, and PayPal Payments Pro, along with a slight (much asked for) enhancement to the order management screen. See the link above for more info.
The download is available from the WordPress plugin page for YAK here.
