send message to all current users

SUGGESTED

Hi All

Has anyone worked out a way to send  a message to all currently logged in users. i need to tell people that the system will be shut down for 15 mins a server reboot at 12pm.

i'm thinking a workflow with the addresses using some function that represents all active logins

seems a fairly basic feature that X3 could do with that I've had in previous systems

any ideas gratefully received