Use the command GET REGISTERED CLIENTS to return an array containing a list of all "Registered" 4D Clients connected to 4D Server. For best results using this command:
1. Turn off the check box in the Connections tab of the Database Properties labeled "Register Cilents at Startup."
2. Place a call to REGISTER CLIENT in your On Startup Database Method. You can pass whatever identification information you wish to this command (e.g. the Current user or Workstation ID).
3. Place a call to UNREGISTER CLIENT in your On Exit Database Method.
These commands were added to 4D to facilitate executing functions between different machines in a 4D Client/Server environment. For more details, see Tech Note 00-27 from June of 2000 "Executing Functions Between Different Machines" by Jean-Yves Fock-Hoon.
https://ftp.4d.com/aci_Technical_notes/ACIDOC/CMU/CMU79837.HTM