Online resources that you should keep shortcuts to and use to access your unowned books:
Add to that your local libraries and interlibrary loans and you have greatly expanded your library. I am sure there are many more useful sites I don't know about. Please add your suggestions.
I've seen you posted these as a reply some years back on another thread, and added the ones that would be useful for my use case. I did notice your original comment (or maybe another commenter) had a couple that aren't on this list:
The only other ones that I've added to my folder on my toolbar are:
Ones that don't really fit into "books that are unowned" but which I have found useful: