In the old days, if you wanted to snoop on a piece of serial gear, you probably had a serial monitor or, perhaps, an attachment for your scope or logic analyzer. Today, you can get cheap logic ...
I have a bunch of Kenwood TK-2100 VHF radios that are re-programmable via the serial port. I have a DOS-based application that works with the radios, but is only reliable with computers with two (2) ...