The principle of having a service in a second application be a slave to the first application can be extended to as many applications as you wish; in other words, one master service can have slaves in many different applications. It is unusual for the master (or a slave) to need to know which application is making an RPC to it; however, for those occasions when you require this information, RPC Manager provides a variable called "RPCManager\CurSourceAppGUID", which contains the binary GUID of the application that sourced the current RPC. Like all the other RPCManager\Cur*** variables, it is valid only for the duration of the RPC subroutine call.