I've described it before: QR code slapped on a book, a patron uses their phone to snap a pic, QR pic takes them to whatever online resource you want them to see.
Here's an example:
Imagine you've just picked up this book in the library, "Chess and the Art of Negotiation", and noticed a QR barcode on it.
You use your gizmo (to which you have already loaded Semacode or Kaywa, etc.) to load the barcode and are taken here:
Hosted resources -- online forums, chess resources, similar books, available e-books, etc. etc. Plus a place for patron comments, so they can add resources you hadn't yet found/ thought of / or approved.
This is a "proof of concept". Sorry I can't give the direct URL yet. Hope you'll work up something like this on your own.