Call out for information: Web shopping carts

I have a Web client who runs an online store. This client has a merchant account and is using a self-hosted Web site and self-hosted ecommerce package/shopping cart called Zen Cart.

Unfortunately, Zen Cart sucks balls, for a number of reasons. It’s slow to be updated (it’s currently at version 1.5, the first update in two years; the progress report on Version 2.0, “Beta Release Postponed Indefinitely,” was made on May 27…of 2009.

My client has gotten fed up with the limitations of this shambling mound of shit and is looking for a new shopping cart solution. The requirements in a new shopping cart are:

– Open source and free or reasonably priced. Shopping carts such as Magento that are priced on a “you must pay this much per year” are not acceptable.

– Must be able to work with and Virtual Merchant as credit card transaction processors

– Must work with PayPal

– Must have a robust and easy-to-use templating system. A system where the template is a complete HTML file with special tags for “insert content here” is preferred. (Seriously, what’s up with all these Baroque, piecemeal templating systems that so many ecommerce and CMS packages use?)

– Must have a very flexible coupon code system that allows great versatility in coupons. For example, “This coupon takes $120 off Product A and/or $160 off Product B,” “This coupon gives you $50 off when you buy Product Z, Y, and W together,” and “This coupon gives you $50 off your total order plus free shipping if you buy Product K plus two accessories.”

– Should be background scriptable. For example, I should be able to click on an “Add one to basket” button on a static HTML page that is not part of the shopping cart, and have the product added to the user’s cart without leaving that HTML page.

– Should allow a user to check out without creating an account, if she desires.

– Must allow for a wide variety of shipping methods (including USPS and FedEx real-time shipping), shipping to many international zones, and by-unit or by-weight shipping prices.

– Must allow ease of updating. Here’s a tip for software designers who need to be smacked: If your upgrade instructions say “In order to update and preserve your customizations, first download a distribution copy of your version of the product and run diff on it to make a list of all the differences between your installed version and the distribution version. Then, open the files in the new version, and…” You. Suck. This is actually the reason so many OS Commerce storefronts are trivial to hack: installing security patches is a protracted nightmare that makes getting a double root canal without anesthesia sound downright attractive.

– Must pass PCI/DSS compliance.

– Edited to add: Integration with SugarCRM would be really, really nice too.

So, any takers? Anyone got a self-hosted cart you like? Shopping carts (other than Zen Cart and the wretched pile of hyena vomit called OS Commerce) to avoid?