It this is say a true thin client these are usually run on Terminal Server (read https://en.wikipedia.org/wiki/Terminal_server and https://en.wikipedia.org/wiki/Remote_Desktop_Services ) which had a notification system built in.
However as many new IT staffers arrive not all are trained or may know what features are already there and ask.
Let's hear more about the thin client or is it a fat client after all?
Please help with suggestions of free softwares with no license or paid version for desktop(thin clients) mass notification system via messaging.

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