SamCart, by co-founder and top internet marketer Brian Moran, is possibly the easiest way to start selling a digital product online. It also has a unique ability to store upsell funnels that are independent of the initial product, i.e. you can easily attach a pre built funnel to a new product.
Sam Cart can be argued to be the best in breed checkout software on the market because they only focus on the checkout and post checkout, unlike all in one solutions such as Click Funnels
. As such it does not have a sales page or optin page builder (and therefore you will need to use and pay for an external landing page software) but does come with pre installed checkout page templates.