Thanks for asking this, that question made me go look it up.
I found https://bookshop.org/info/ebooks
I thought you could load bookshop.org eBooks onto a Kindle, but it seems they have their own DRM and you need to use their own app…
Some of their books are DRM free, but not all. I thought they all were, but it turns out I was wrong.
So… maybe even bookshop.org isn’t the best option for Kindles.
I guess there really is only one option left…
To all the people who are saying “I’ll just pirate books,” you are aware you can buy eBooks from places that aren’t Amazon, right?
Have a look at https://bookshop.org/ebooks You can buy books/eBooks and support local bookstores that aren’t Barnes & Nobles or Amazon.
I’d suggest you download/archive your Kindle books and then buy your eBooks from elsewhere. You can still load those onto your Kindle.
Saying “I’m going to pirate because one specific website is changing its policy soon,” is pretty stupid.
EDIT: Turns out I was wrong about bookshop.org, you actually can’t load their eBooks into a Kindle. You need their app since they have their own DRM. Looks like I got all worked up about something without looking it up first.
Note-taking app. Each note is a markdown file, so you can add formatting.