For a stand-alone UA server the uaPLUS.Net4.exe is the main application.

The server developer only needs to develop the application specific device/database handler plug-in DLL .
Users of the Advosol server toolkits for classic OPC may be able to use the plug-in DLLs from their Classic OPC DA/AE or HDA servers. In this case no development effort is necessary.
Implementation possibilities are restricted because all application specific features need to be implemented in the plug-in DLLs that have a pre-defined uaPLUS.exe interface.

The development step depend on the needed server functionality:

Server with DA (Current Data) functionality

Server with AE (Alarms&Events) functionality

Server with HDA (Historian) functionality