I am looking to get a shopping cart system, used as an include file through the entire website.
add to cart one product at a time or multiple products (by check boxes) switchable on the back-end
cookies or session based
calculate shipping based on price or weight
calculate tax (by state or static value)
product attributes (size, color, etc. if the product has any)
check stock level
update stock level
use of coupons
you get the ideea.
all requirements of a shopping cart, easy to implement into any website/s