Popup Message is a small tool to display SMB-Messages. It receives all network messages and shows them like the Messenger service on Windows NT systems. It is compatible with the 'net send' command on Windows NT/2000 systems, with programs like WinPopup on Windows 9x and samba.
There are a lot of WinPopup clones out there. And all of them implements a lot more features than the original. Popup Message does not have as much features as WinPopup has. But that may be its advantage.
Differences to WinPopup:
For stopping Popup Message simply open the taskmanager by pressing [Ctrl]+[Alt]+[Del], select the Popupmessage-task and kill it.
If you are looking for a free, full featured WinPopup replacement have a look at RealPopup.