This is really nice. I have a personal book library app too, also in PHP/MySQL, though as a former library employee I ended up focusing more on cataloguing and

This is really nice. I have a personal book library app too, also in PHP/MySQL, though as a former library employee I ended up focusing more on cataloguing and checkout. (I import from the Library of Congress API rather than Amazon, for example.) Also, I wrote a bunch of me-specific hacks and am still working on patching all those out (ten years later, lol) with the intention of making it usable to others and publishable as a Sandstorm app. I'm also still in the process of open sourcing it, mostly for some of the same reasons you mentioned. Right now my library-specific code is open sourced but the core framework I built it on top of is not yet: I've only recently begun modernizing the security code. I would love to see your code someday if you ever get around to sharing it though!