Adding products to the cart from external entity
From AbleCommerce Wiki
This functionality can be easily incorporated into AbleCommerce store. For example there may be some situation in which you want an affiliate or an external entity to allow customers to add products to the cart from their website.
This can be done with two things, a special link which will be placed over the external entity website and will contain the ProductId in it and secondly a user control which will on the web page refereed by the that special link at your store.