http://www.magentocommerce.com/
They released it today as promised.
My take on it: I’ve played with a few betas. It looks like an excellent product. However, there were still some pretty major bugs in beta version just a few weeks ago. This is a major piece of software, and it’s almost certain there will be significant bugs in there. For those keen to try it I’d recommend waiting at least three months to let the dust settle and to let the worst of the bugs be knocked out.
Also check support for your preferred payment gateway(s). There are still some major omissions, and documentation is still thin on the ground.
In short, great product, but wait.