As I said - this is all semantics. In the context of RapidWeaver, a theme has a different meaning to examples of WordPress or ThemeForest themes.
Bootstrap and Foundation are frameworks yes, but a RW theme made from them has a lot of integration and other elements that make them work easily for users in RapidWeaver. These are so much more that if you just included the framework CSS and JS.
In addition, there are the stack sets that many people supply with their “framework themes” that allow users to easily use the framework core features in a drop in manner and, importantly, without the traditional code replication of stacks by utilising the framework classes.
Any theme (RW or otherwise) is just a layout and usually a menu plus other optional features such as pre-built sliders etc. The RW framework themes are just the same except the user has more control over what goes where as these components are encapsulated in stacks.
Never the less, RW users understand the word theme to mean a template of one sort or another, that can be selected via the Themes menu and will give them some functionality or other. Nothing more, nothing less. Beyond that anything is a purely an a priori discussion.
??? I’m not sure why you would expect a pre-built theme specifically for selling books on RW. That’s a tiny tiny market. And themes (as some have stated above) are not geared to very specific uses like that. They are general “looks” for a website. I’d guess there are many different themes one could use for creating an online bookstore.
More of the trick would be how do you sell the books? There are a few different products for that: Cartloom, RapidCart, and some others. Which is best for selling “stuff” like books is something you’d have to investigate.
Gumroad is great for digital products.
Shopify had issues, plus the costs were prohibitive given low volume.
Any digital product that required a picture, a gallery (if there’s more than one product), a link to a product page, and a link to purchase. So it’s not just books, it could be:
music
anything on Etsy
clothing items
tools
automobiles
oil rigs