Dear friends,
the official download section for Virtuemart 3 is available here: Virtuemart download section
One Page Checkout for Virtuemart is now fully compatible with Virtuemart 3. You can check our development demo here: http://vm2.rupostel.com/purity (it has always the latest Joomla 3.x and Virtuemart 3 )
The Virtuemart 3 on Joomla 3 is now the main developement platform and is the most supported version combination.
Best Regards,
RuposTel.com Dev Team