Several different programs are available, covering people who read only a book or two each month to those who read many, or for a family of readers to pay a single fee for all members combined.
Bookswim claims not to be in direct competition with libraries. In fact, it offers a program to libraries which Bookswim claims will alleviate the not infrequent problem when a rush of requests for a particular item exceeds the inventory in the library.
I am inclined to think that if this new book rental program survives and thrives, that it will be a bigger threat to the large booksellers than to the public libraries. After all, it is hard to compete with free! Should be interesting!