Forum Moderators: buckworks
As for carts that offer this, a quick google search for 'Shopping Cart COD Payment' shows carts such as Fortune3, ihtmlmerchant, Monster Commerce, Dansie, Product Cart claiming to support this service etc.. I'm not sure to what extent any of them are integrated with the couriers to automatically setup the COD request when arranging the delivery manifest.
Payment from worldwide - this is more to do with whatever payment system you use. I would expect Cash On Delivery Payment would be limited by UPS/FedEx etc to the same country as the sender (but have no experience of this!)
As far as just selling one of each item, most good carts allow for inventory management, and give the option for products to be automatically hidden when the stock is zero.
jules.