We are having an OpenCart website version 1.5 in development.
We want products that can be just printed. No downloads/no shipping.
In a way, the product's invoice should be printable.
When a user buys a product, he will checkout and once the payment is completed, he will be redirected to the website where his invoice will be available to be printed. And the same invoice will be emailed to him in PDF format.
The features are already there in Opencart. They just need some proper arrangement.