Project Server 2007 Client Access Licenses (CALs) are required for each device or user that accesses the features and services of Project Server 2007, for example to use the thin Web client Project Web Access, Project Web Parts in SharePoint, or connecting customized client interfaces.
The CAL enables Project Web Access, the web client to the EPM Solution, which enables users to view, analyze and report on information including timesheets as well as create project proposals and activity plans. This also includes the administrative user interface.

Please refer to the licensing brief “Multiplexing — Client Access License (CAL) Requirements” and the Product Use Rights agreement for additional details on CALs.