-Titles borrowed by one user at a time

-Expire after a set period of time

-Metered by time, checkout, or both

-Titles can be borrowed simultaneously until budget runs out

-Pay only when title is borrowed

-Title can be borrowed simultaneously

-Usually expire after a set time

-Project Gutenberg titles never expire

-Titles borrowed by one user at a time

-Never expire from collection

-Titles are rented to a specific set of users for a predetermined length of time

-Titles are automatically checked out on chosen start date.