What the difference between single site usage, developer and multi site usage versions ?

Each specific version of Booking Calendar can be single site usage version, developer or multi site usage version.
Single site usage version, possible to install and activate only at 1 specific website.
Developer edition version, possible to install and activate at 2 different websites. Its can be test (developer) server and live website.
Multi site usage version, possible to install and activate maximum on 5 different websites.