1.5.1, 1.5.2, 1.5.3, 1.5.4
You've got a store that sells only virtual products, so none of your products require shipping information. You still need to collect your customer's address-related information, whether for tax-determination or other purposes.
This plugin modifies the display of the checkout process, recognizing that the checkout_shipping page will never be used; the result is that your checkout process is reduced to checkout-payment choice followed by checkout-confirmation. The invoices generated by your store's admin contain no references to shipping addresses. There's no "Packing Slip" link on your admin's Customers->Orders page, since there's nothing to pack!
Note: This plugin supports Zen Cart versions 1.5.1 through 1.5.4; if your store is running Zen Cart 1.5.5 or later, you'll need to use All Virtual Products (No Shipping) -- ZC 1.5.5+ instead.