The Professional Edition is designed for small and medium-sized teams. In addition to the basic functionality included in the Essential, you can view passwords, single sign on agents, and reporting and auditing.
The Enterprise Edition is intended for larger teams and company-wide roll-outs. The features of the Professional Edition are supplemented by Active Directory Integration, temporary releases as well as the possibility to include a second factor in the registration.
The Enterprise Plus version is designed for an unlimited number of users. It includes an API, as well as Auto Discovery and Password Reset, which are the essential features for large corporations.