Also, I've seen a surprising number of DRM free novels turn to itch.io if you are looking for a "non-traditional" approach, but someone to handle a lot of the "storefront basics" for you. This seems to be an extension of itch.io becoming a major hub for indie TTRPGs, because a indie designer can just throw a simple PDF (and maybe a DOCX or an EPUB) on itch.io as opposed to the effort that DriveThruRPG/RPGNow want in PDF formatting. Then a few TTRPG related novels started using the platform, and like I've said I've seen a surprising set of novels that aren't even directly game related at this point. itch.io's flexibility in what they will publish/host is an interesting strength (though makes it a bit more caveat emptor than a traditional retailer from a consumer side searching for interesting books).
1. Smashwords. They've been around for a long while now, and the publishing system isn't as snazzy as KDP. You input a Word file (.doc, not .docx) and - assuming their "meatgrinder" accepts your document's formatting - the site outputs epub, mobi, pdf, rtf and various other minor format versions. The book then gets published on the Smashwords site.
2. More importantly, Smashwords has a number of partnerships in place - key ones being Apple Books, Kobo, and Barnes & Noble. This ability to ship directly into Apple Books is the MAJOR reason why I continue to use Smashwords as that's where the majority of my 'sales' happen.
3. You can then download the epub and mobi files and upload them to the other two mainstream channels as followup actions: KDP for all Amazon/Kindle distribution; and Google Play Books for the all-important distribution across Android devices.
4. For the cherry on top, I sometimes also offer books in hardcopy. KDP has (I think) processes in place to convert an eBook into a hardcopy book. But mostly I use Lulu because they've been around for a long time, I like their publishing flow, and <insert-vitriolic-anti-kdp-rant-here />!
 https://www.smashwords.com/ - Smashwords landing page
 https://www.smashwords.com/books/view/52 - the Smashwords Style Guide - I guarantee that you come to love-and-hate this book in extreme-yet-equal measures.
 https://www.smashwords.com/books/view/11163 - I have never knowingly turned down an opportunity to spam the link to one of my books. It's free. Enjoy!
 https://www.lulu.com/ - Lulu.com landing page
I believe ddevault published his Wayland book this way.
An important feature I like is the ability to update the books (due to s/w versions, typos, adding new content, etc) and notify the users regarding the new version.
Another feature for both sites is that customer can pay more than the price of the product. And that does happen often enough to make it a highlight of using their site. But this may probably apply more for technical books than fiction.