Marketplace feature / selling single items

I'm working on a project with Marketpress on Multisite Network and looked at this website in your 'featured' section

Can you please tell me how they created the 'Marketplace' layout and also if you go to the link above and click 'start selling' - that is incredible - how can I add that feature where people can sell a single item and just register with their paypal account??

These are great features!