Most WordPress shops are a general purpose ecommerce platform wearing a theme. They assume you are selling physical stock, then bolt digital goods, subscriptions and services on afterwards as extensions, each with its own settings screen and its own idea of what a product is.
Store starts from a different assumption: a product is a thing you sell, and what kind of thing it is should change how the page behaves rather than which plugins you had to buy.
A product that cannot be bought says so
Take a product with no price. There are two ways to arrive there. Call for price is the deliberate one, ticked on the product because the job is quoted rather than listed. A price of zero is the accidental one, and it is treated the same way rather than printing a currency symbol and two noughts, which does not read as ask us, it reads as free.
Either way the shop stops the sale everywhere at once. The grid shows the note instead of a figure, the product page shows it where the price would stand, and the cart refuses the line. There is no buy form on the page at all, because a quantity field over a button nothing can press is a page that reads as broken.
A free download is the opposite case and is handled as such. It has a price, and the price is nothing, so it stays buyable and the order is still raised. The customer gets it in their account and gets told when a new version lands.
Pre-orders are not sold out
A pre-order is out of stock by definition, because it does not exist yet. Reading the stock column alone marks it unavailable, which tells a customer not to bother with the thing you are advertising. The stock line, the button and the cart all ask the same question, so a product reads Pre-order on the shop, on its own page and in the basket.
The rest of it
Coupons, shipping zones, tax rates, couriers, order emails and sales reports are all in the box, and so are subscriptions, loyalty points, reviews and digital downloads with signed links. Payments go through Stripe or PayPal. Every currency the shop takes carries its own symbol and its own placement.
None of that is an extension. It is one plugin, and switching it off leaves your order history exactly where it was.