OfficePopup 1.23 (Windows)
Source: LionClock Software
From the developer: "OfficePopup allows you to send announcements and alert to anyone on your local network (LAN). OfficePopup works on any TCP/IP-based network and doesn't require configuration. In other words, it can be used immediately after installation. "By default, OfficePopup allows users to send and receive messages. However, in case you would like to use OfficePopup to broadcast messages only, you can specify that during the installation. This way, you can be absolutely sure that particular users won't spend most of their day sending messages to other people. Advanced users will find that OfficePopup is a great replacement for WinPopup utility that was supplied with Win9x/NT and is unfortunately missing in the recent versions of Windows such as Windows 2000 and XP."