well,
you do not even need a special software for this if you just
want to analyze a serial port for txed and rxed data.
You can use another computers serial port for this.
If the communication is half duplex than it is OK. This
communicaiton can be traced from another computer.
I mean both txed and rxed data can be traced at the same time.
You just need a simple and specific rs232 cable.
Cable should have rx tx and gnd only.. The tx and rx lines
must have a diode wired to each other and they both will go directy
to the rx of rs232 db9 connector. (this db9 is the place you sniff the protocol)
You will plug this cables tx,rx and gnd parallel to the communication you
want to sniff.
As you have a diode in tx and rx the serial ports cannot be damaged.
And the perfect benefit is that you can trace both the rxed and txed in its
respective order.