Serial Port Sniffer ActiveX Control 

Serial Port Sniffer is a powerful advanced ActiveX Control that allows your application to sniff (fully monitor and edit data flows) serial port in your system. Serial data streams can be easily monitored and edited directly from your application.
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Bill Serial Port Monitor 

To monitor (bi-directional) Serial communication RS-232 between two devices without physical cable, you can use the freeware Bill Serial Monitor. This freeware enable you to view, log, test and analyse the activity of the serial RS-232 port.
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