This one is for the rebels. If you buy a book, download it as an AZW file (or remove DRM using Calibre—yes, it’s a thing), you can email it to anyone. But Amazon’s terms of service frown on this like a librarian shushing you. Technically illegal? Probably. Morally murky? Depends on why you’re doing it.
How to Share Amazon Kindle Books with Family Members - Phandroid
I won’t give you the full how-to because I don’t want Jeff Bezos knocking on my door. But know this: it works. You can share any DRM-free file via email to “Send to Kindle.” Just make sure the other person has their “Send to Kindle” email address set up. (It’s in your Kindle settings, under “Preferences.”)